I ran across a scenario where I wanted to follow a twitter user via an RSS reader the problem that I had was that google reader (unlike some of the other readers) did not like the format of the API as addressed in the following blog post
http://thenextweb.com/twitter/2011/06/23/how-to-find-the-rss-feed-for-any-twitter-user/
Luckily someone in the comments did have a link to the standard for the “old format” which appears to still work as of the time of this post
The format of the URL is as follows, this worked without a problem for me
http://twitter.com/statuses/user_timeline/{USERNAME}.rss