It's nice though that someone famous talks about bitcoin, I've seen his tweets retweeted about his bitcoin related tweets. So he has sparked some wondering of bitcoin to some of his fanbase.
Any celeb mentioning it is good and especially great exposure on Twitter and Facebook etc.Each time it's posted it has the potential to reach millions and will at least peak the interest of a lot of people at least.
It really needs to be more then them just mentioning it. It needs to be more of an endorsement.
The MSM has reported on bitcoin enough so that most people at least know somewhat about bitcoin or at least have heard of it, which is what a celb mentioning it would accomplish.