In the past, all Streaming API feeds filtered some "low-quality" users. Now Tweets from all non-protected ("non-private") users explicitly requested on the filter method with the follow parameter are also delivered. Only protected users' updates will be absent from track
follow. You may begin phasing out special case REST fallbacks for these users. This should resolve one of the major integration complications on the Streaming API.
All other streams and predicates remain unchanged. For example, the firehose, sample, retweet, and link streams as well as track and location predicates on the filter stream will continue to filter users for quality.
-John Kalucki
http://twitter.com/jkaluckiInfrastructure, Twitter Inc.