It looks like when I try to get the comments of a user that has "a huge number" of comments, I get a 500 error.
Jon Skeet's comments, 500 error: http://api.stackoverflow.com/1.0/users/22656/comments
Whereas a smaller query works just fine:
rascher's comments: http://api.stackoverflow.com/1.0/users/3788/comments
I even get this error when I set a small page size. What is the threshold for "this is too many comments for the API to deliver?" Could we obtain some metrics - like the number of comments or paging thresholds - before the request is rejected outright?