From Weird Science bully to Iron Man

Ain't It Cool News broke this yesterday, and I guess it's been confirmed all over the press today--Robert Downey, Jr. has been cast as Tony Stark in the upcoming Iron Man movie.

I'm not sure what I think about this casting choice. Robert Downey, Jr. isn't someone I would think about for any superhero role. This reminds me a bit of Michael Keaton being picked to play Batman. That turned out OK--not great, but acceptable. I guess Robert Downey, Jr. can bring his own personal demons with substance abuse to the role, though, as I'd expect some heavy scenes about Tony Stark and his alcoholism assuming Marvel doesn't chicken out.

Anyone have any thoughts? Honestly, I can't have that much of an opinion considering I didn't read all that much Iron Man in my day.