In accordance with our previous announcement, we have completed the change to Search API rate limiting response code. This change allows downstream systems to more appropriately respond to rate limiting. The original announcement follows:
We're changing the response code sent back by the Search API when the
rate limit has been exceeded. At present, it is impossible to
distinguish rate limit responses from other error conditions in
responses from the Search API -- this is what we're trying to fix.
Starting Monday, January 18th, 2010 the Search API will respond
with error code 420 in the event that the number of requests you have
made exceeds the quota afforded by your assigned rate limit.
If you have any questions, please feel free to post them on twitter-development-talk.