Niall Kennedy has a post about the newly released Yahoo! Pipes. As he says:

"Yahoo! Pipes lets any Yahoo! registered user enter a set of data inputs and filter their results. You might splice a feed of your latest bookmarks on del.icio.us with the latest posts from your blog and your latest photographs posted to Flickr."

He also warns about possible implications for web publishers:

"Yahoo! Pipes makes it easy to remove advertising from feeds or otherwise reformat your content."

Note: As yet, I have not been able to access the site. Interested to learn if anybody else has and what their experiences have been.