I imagine a /status method would not be too hard, and is crucial in both testing and deploying applications.
Imagine an application that updates a database with new questions. It can query the /status method to correctly time it's calls so that it can make it through the day.
I would also consider whether this call should count towards the limit. Twitter, for instance, doesn't count a /status call against the limit.
Actually, it is included in all headers. From Chrome, here is what I get back:
Cache-Control:private
Connection:keep-alive
Content-Encoding:gzip
Content-Length:5158
Content-Type:application/json;
charset=utf-8 Date:Thu, 20 May 2010
23:18:10 GMT Server:nginx
X-AspNet-Version:2.0.50727
X-AspNetMvc-Version:2.0
X-RateLimit-Current:298
X-RateLimit-Max:300