New Twitter doesn't have a button on users' profile pages anymore that allows you to subscribe to their messages as an RSS feed. When you're on a profile page and try to subscribe using your browser's built-in feed subscription mechanism, you get a feed of your own favorite tweets (WTF!). You can still get a feed of a user's updates by doing the following:
HTH!
- Grab there user name (e.g., mashable).
- Punch it into idfromuser.com to get the associated user ID.
- Prepend "http://twitter.com/statuses/user_timeline/" to that ID.
- Append ".rss" to that.
HTH!