Update:
I generally try to back any claims of bugs and shortcomings with evidence.
I have prepared a test page which you, dear Stack Overflow staff and my fellow developers, can use to ascertain for yourselves whether the api throttle is performing to spec.
You can find these tests here: http://soapi.info/Code/JS2/latest/Tests/ThrottleTests.htm
If you choose to run the tests please use the 'Upload Results' button to upload your results into the aggregated dataset which can be viewed/downloaded here: http://soapi.info/Code/JS2/ThrottleTestIndex.aspx
As of 9/5/2010 I am still not satisfied that the throttle is performing to spec. It seems that we may be edging towards the published specification of 30 requests per 5 seconds window, but the results are inconsistent, with the most reliable rate @ 30 requests per 6.5.
I raise this issue not because I am obsessed with making the most possible requests per second as has been repeatedly implied. I raise this issue because as software developers we deal with specifications. We spend valuable time writing code to specification to ensure the best possible quality of code and user experience. If the upstream data source our apps rely upon does not perform to specification we all suffer - our users are denied the reliable awesomeness of our efforts and are likely to judge those efforts and find them wanting regardless of true merit.
original post
The throttle is acting up again.
Request rates are well within published guidelines.
see https://stackapps.com/questions/1433#1448
GET /1.0/users/moderators?key=my-key&jsonp=Soapi._jsonp133 HTTP/1.1
Accept: */*
Referer: http://localhost:17742/AlphaQuickStart.htm
Accept-Language: en-US
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; Tablet PC 2.0; .NET4.0C; .NET4.0E)
Accept-Encoding: gzip, deflate
Host: api.stackapps.com
Connection: Keep-Alive
HTTP/1.0 503 Service Unavailable
Cache-Control: no-cache
Connection: close
Content-Type: text/html
Too Many Requests - Stack Overflow
We're sorry...
There are an unusual number of requests coming from this IP address.
To protect our users, we can't process any more requests from this IP address right now.
We'll restore access as quickly as possible, so try again soon.
If you believe you have reached this page in error, contact us.
The nginx proxy seems to have been removed so either there is no api throttle or there is a new throttle that does not work.
reports of successful tests are puzzling.
01 throttle: 2010-07-23 23:17:31.458 - request dispatched: interval: 1282630651458ms - http://stackauth.com/1.0/sites?key=xxx 02 throttle: 2010-07-23 23:17:31.680 - request dispatched: interval: 222ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&key=xxx 03 throttle: 2010-07-23 23:17:31.696 - request dispatched: interval: 16ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=1&key=xxx 04 throttle: 2010-07-23 23:17:31.706 - request dispatched: interval: 10ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=2&key=xxx 05 throttle: 2010-07-23 23:17:31.715 - request dispatched: interval: 9ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=3&key=xxx 06 throttle: 2010-07-23 23:17:31.724 - request dispatched: interval: 9ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=4&key=xxx 07 throttle: 2010-07-23 23:17:31.733 - request dispatched: interval: 9ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=5&key=xxx 08 throttle: 2010-07-23 23:17:31.741 - request dispatched: interval: 8ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=6&key=xxx 09 throttle: 2010-07-23 23:17:31.749 - request dispatched: interval: 8ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=7&key=xxx 10 throttle: 2010-07-23 23:17:31.756 - request dispatched: interval: 7ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=8&key=xxx 11 throttle: 2010-07-23 23:17:31.765 - request dispatched: interval: 9ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=9&key=xxx 12 throttle: 2010-07-23 23:17:31.775 - request dispatched: interval: 10ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=10&key=xxx 13 throttle: 2010-07-23 23:17:31.786 - request dispatched: interval: 11ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=11&key=xxx 14 throttle: 2010-07-23 23:17:31.796 - request dispatched: interval: 10ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=12&key=xxx 15 throttle: 2010-07-23 23:17:31.807 - request dispatched: interval: 11ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=13&key=xxx 16 throttle: 2010-07-23 23:17:31.820 - request dispatched: interval: 13ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=14&key=xxx 17 throttle: 2010-07-23 23:17:31.833 - request dispatched: interval: 13ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=15&key=xxx throttle: 2010-07-23 23:17:31.846 - active queue full 18 throttle: 2010-07-23 23:17:31.871 - request dispatched: interval: 38ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=16&key=xxx 19 throttle: 2010-07-23 23:17:31.885 - request dispatched: interval: 14ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=17&key=xxx 20 throttle: 2010-07-23 23:17:31.897 - request dispatched: interval: 12ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=18&key=xxx 21 throttle: 2010-07-23 23:17:31.910 - request dispatched: interval: 13ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=19&key=xxx throttle: 2010-07-23 23:17:31.922 - active queue full 22 throttle: 2010-07-23 23:17:31.999 - request dispatched: interval: 89ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=20&key=xxx 23 throttle: 2010-07-23 23:17:32.012 - request dispatched: interval: 13ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=21&key=xxx 24 throttle: 2010-07-23 23:17:32.028 - request dispatched: interval: 16ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=22&key=xxx 25 throttle: 2010-07-23 23:17:32.042 - request dispatched: interval: 14ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=23&key=xxx 26 throttle: 2010-07-23 23:17:32.055 - request dispatched: interval: 12ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=24&key=xxx 27 throttle: 2010-07-23 23:17:32.068 - request dispatched: interval: 14ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=25&key=xxx 28 throttle: 2010-07-23 23:17:32.078 - request dispatched: interval: 10ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=26&key=xxx throttle: 2010-07-23 23:17:32.095 - active queue full 29 throttle: 2010-07-23 23:17:32.116 - request dispatched: interval: 38ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=27&key=xxx 30 throttle: 2010-07-23 23:17:32.128 - request dispatched: interval: 12ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=28&key=xxx throttle: 2010-07-23 23:17:32.136 - waiting 4822ms 31 throttle: 2010-07-23 23:17:36.964 - request dispatched: interval: 4836ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=29&key=xxx throttle: 2010-07-23 23:17:36.998 - waiting 182ms 32 throttle: 2010-07-23 23:17:37.181 - request dispatched: interval: 217ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=30&key=xxx 33 throttle: 2010-07-23 23:17:37.203 - request dispatched: interval: 22ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=31&key=xxx 34 throttle: 2010-07-23 23:17:37.225 - request dispatched: interval: 22ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=32&key=xxx 35 throttle: 2010-07-23 23:17:37.247 - request dispatched: interval: 22ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=33&key=xxx 36 throttle: 2010-07-23 23:17:37.272 - request dispatched: interval: 25ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=34&key=xxx 37 throttle: 2010-07-23 23:17:37.299 - request dispatched: interval: 27ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=35&key=xxx 38 throttle: 2010-07-23 23:17:37.321 - request dispatched: interval: 22ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=36&key=xxx 39 throttle: 2010-07-23 23:17:37.342 - request dispatched: interval: 21ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=37&key=xxx error: /tags failed http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=34&key=xxx --> @ 23:17:37.272 throttle: 2010-07-23 23:17:37.375 - request dispatched: interval: 33ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=38&key=xxx error: /tags failed http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=35&key=xxx error: /tags failed http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=33&key=xxx error: /tags failed http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=36&key=xxx throttle: 2010-07-23 23:17:37.443 - request dispatched: interval: 68ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=39&key=xxx error: /tags failed http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=37&key=xxx throttle: 2010-07-23 23:17:37.473 - request dispatched: interval: 30ms - http://api.meta.stackoverflow.com/1.0/tags?pagesize=1&page=40&key=xxx
waitintervals of more than 7 seconds between any n+0=>n+30th request. thank you.