Our operations team has informed me that we'll soon be blacklisting IPs originating at hosting provider The Planet (http://www.theplanet.com/). We've attempted to resolve a number of abuse complaints with them over a long period of time and have not received an acceptable response. If your service or application is hosted at The Planet, please be aware that this will impact your ability to talk directly to the Twitter API.
-- Alex Payne - API Lead, Twitter, Inc. http://twitter.com/al3x
