Given that so many Nader voters in 2000 said they probably would have voted for Gore under other circumstances, I don't think it's too much of a stretch to propose that had Nader not been involved Gore might well be president today.
Honestly, it wouldn't have taken that many. If you assumed that one percent of the Nader voters in Florida had voted for somebody else (instead of not voting at all if Nader wasn't a choice), and that about 60% of
those people had voted for Gore instead of one of the other guys, then Gore would have indisputably carried Florida.
Or that's what I heard, anyway. I guess we could dig up the data and do the math ourselves.