I do look forward to Donna, as long as they keep her "edge". I think that one of my biggest problems with the way that the Companions have been handled, both of them so far, is that the longer they're with the Doctor, the more they lose their independence as people and become orbiting satellites of the Doctor. The things I like about Donna, her sparkiness and no-nonsense attitude, are things I'm afraid she'll lose if she takes up Tardis residence.