<a href="http://apiwiki.twitter.com/Rate-limiting" rel="nofollow">http://apiwiki.twitter.com/Rate-limiting</a><p>and<p><a href="http://groups.google.com/group/twitter-development-talk/msg/fa03b3c64d18ac5a" rel="nofollow">http://groups.google.com/group/twitter-development-talk/msg/...</a><p>should help.