I started playing around with Riffs today, a public user reviews site that let's you post and comment on anything.  It's a very simple idea with a really good domain name and a tight user interface. 

I'd like to say that I thought of doing something very similar, but that's a meaningless claim since I have nothing to show for it.  Somebody actually delivered, and, damn, they did a really nice job. 

They even have a bookmarklet and a "Riff Roll".  If they opened their APIs so that other sites could read and write to this system, then I think they would see mass adoption in short order.

Regardless, well done whoever you are.