While Yahoo Buzz did steal Digg's concept of social news, I'd say it's a valid competitor just because of the fact that it's hacked by Yahoo.

With that said, I'm frightened by the implications of some newbie blogger sites being hit with the traffic that flocks to Yahoo. Servers will melt around the world. ;-)

The prospect of giving small, interesting sites the opportunity to hit Yahoo's homepage is very, very cool.

Yahoo adds Buzz! - (the possibility to get on Y!'s homepage)

- Digg.com's value plunges 30-40%

- The idea wins when backed with a great re-ward, I look to MSN and CNN etc to do similar things.

Proving that your publicity is more important than your product, most of the time.