UserStream is sometimes a little challenging to get going at first, but once everything is in-place it seems to work well. Here are a few tips:
1. Use OAuth authentication. Here's the FAQ in case you need help: http://linqtotwitter.codeplex.com/wikipage?title=LINQ to Twitter FAQ.
2. Try getting OAuth working with a simple REST API query first. i.e. do a search. That will help iron out OAuth issues before moving on to the more complex task of streams.
3. Try to use the samples from my downloadable code first because they have been tested.
4. If you encounter a lot of errors when first trying to connect, wait a while because Twitter might temporarily block your IP (security measures).
5. Follow inner exceptions to pull out all of the error information.
6, Use Fiddler for debugging the HTTP responses from Twitter.