If you have an RSS feed where the links themselves point to other RSS feeds, this pipe will aggregate all the posts into one feed sorted by post time (I think). This was intended to be used with in conjunction with a strategy of bookmarking feeds of interest via a service like Delicious. To use the pipe, I submit the URLs of feeds I like to Delicious and tag them with something distinctive, and then I submit the corresponding tag page to this pipe. The result is an aggregated feed of all the posts in the feeds I've tagged. At least, that's what i hope. As a parameter, you can submit a webpage; it will try to autodiscover your feed.
Pipe Web Address: http://pipes.yahoo.com/nathanrein/feedoffeeds