'My Web', is Yahoo's new personal search engine integrated with Yahoo! Search...from their blog:
"You can publish your My Web links via RSS and, of course, there’s an API for My Web published on YSDN. We're also experimenting with Attention.XML as a way to ship around My Web data. To try it out, go to any My Web RSS feed and replace the "rss.xml" filename with "attention.xml". As is often the case with brand new ideas, we haven't really figured out how exactly this should work, but there’s only one way to find out."
This is the first major player to try something out with Attention.xml that I'm aware of...more to come me thinks...