Do I ever go back and read what I've tagged as ToRead? Nope. 43 items later, I don't think I've ever gone back to read something...
Still waiting to see the future of Yahoo! Primarily because of Flickr, but they run del.icio.us too, and I think it would be extremely easy for Microsoft to inadvertently damage del.icio.us whilst trying to do something cool that they think people want.