I use bloglines to read weblogs. I recently added a site that posts different deals on the web every day because I was going to buy a new monitor. Anyway, I still like to see what is going on, but there are a lot of deals I'm not interested in. I'd really like to be able to filter the results.
Bloglines doesn't have any filtering capability, but I could create a proxy server to do the filtering for me. So for example: Instead of giving bloglins http://feed.com/atom.xml I would give it http://myproxy.com/blogfilter/feed.com/atom.xml. My 'blogfilter' application would make the request to feed.com, get the data, filter stuff out and return the results.
Somes services that do this already: