I've never really needed to do much with RSS feeds besides read a few news sources and blogs easily. However, today I came across the need to mashup several sources and then filter them - a search on multiple RSS feeds, based on the content of each. I went through a few barebones web services, and then I came across Yahoo Pipes - I was floored. The interface is quite amazing - aesthetically pleasing and easy to use but amazingly powerful and versatile. You can filter based on a million things from the title, description, density, length, and more, and easily put together all your search criteria in a visual format and then publish it. Even nicer, you don't have to keep using Yahoo! anymore - you can use whatever RSS tool you'd like and just subscribe to the single feed. My weapon of choice is NewsNetWire for my iPod Touch. Way to go guys!