Wow, I did NOT know George Harrison played on that Belinda Carlisle song and now it totally makes sense, hearing it. The man had such a lyrical ear.
For the most part, though, celebrity guitarist guest spots don't turn out well, in my experience. Like Beck in Private Dancer. Meh. And though Michael Jackson was scene-chasing by getting EVH to solo, I think it just doesn't suit the song (and I agree with someone somewhere who once said it sounded like a guitar phrase falling down some stairs).