Google Reader Filter is a Greasemonkey script that lets you define a list of keywords you're interested in and a list of uninteresting keywords. The script highlights the posts that include your favorite keywords in the title and grays out the posts that contain keywords from the blacklist. You can use regular expressions for defining complex restrictions, like dates or long titles.
The script doesn't remove posts, so it's more like an automatic highlighter. Feed Rinse has another approach: add a feed, define a list of simple rules for filtering and you get a filtered feed that can be added to your feed reader. For some reason, I couldn't subscribe to Feed Rinse's feeds in Google Reader, even though they were valid and any other feed reader accepted them. Hopefully, it's just a temporary problem.
You could also use a Yahoo Pipe that lets you define a list of keywords that are potentially interesting. So if you enter gmail, google calendar as a filter, the pipe will obtain a list of posts that contain Gmail or Google Calendar. After running the pipe, click on "More options", select "Get as RSS" and subscribe to the feed. As Yahoo doesn't allow you to change the feed's title, you should rename it in Google Reader.
