Twitter rate limiting was doing some funky stuff.  Was using the Search API and getting 503, which means you are getting rate limited even though the error response is Server Too Busy.  Discovered their rate limiting API, which you can call at http://twitter.com/account/rate_limit_status.xml to find out what was going on.  When this was called from a browser, it return 150. But when called using WebClient and passing a User Agent string with a URI, the api returned with 20000 as the upper bound although it didn't seem to respect that. Another funny thing is that, although I'd send a single request, it would ding me for multiple requests.  Not sure what is going on there under the hood.