It is called Feedsifter and can be found here
You just put in the URL of the site and then type in the keywords you are interested in and Feedsifter creates a second feed that you can subscribe to. Now you have a feed tailored to your interest!
If you have a google account the easiest thing in the world is to sign in. Go to igoogle and click add stuff . Looking down on the left sidebar you will find a choice for entering a url – paste the feed URL that feedsifter created there and you will now have this feed show up directly on your igoogle homepage.
I have often used del.icio.us to create a feed of bookmarks on a specific subject. Today I created one for googledocs and using Feedsifter I had it make a new feed that would show me only googledoc bookmarks that contain spreadsheet and/or form. Now I have an area that helps me keep up with new blog posts on Google spreadsheets. This won’t be a perfect solution but it helps me narrow down some of what shows up in my reader now.
This tip came from The Simple Dollar – thanks for a great hint!