Just tried it, really cool tool. I hate subscribing to the feeds of big tech news sites because there are a lot of posts I don't care about. Being able to filter it like this is really useful. And in 4 hours! Good job.
There's a number of existing services (like http://www.feedrinse.com/) but I really wanted to make it as simple as possible (no sign ups, no fancy UI, easy to use and free).