I like Novak, but I think it was over the top in this case, considering the relative difference in rank, the relative earliness in the tournament, the fact that he possibly skated by on a bad line call, etc. It would've been classier not to do it.
On the other hand, for tournament finals, or where you've been battling it out with someone who's approximately your equal, I think it's fine. It's hard to put into words, but one feels earned and one feels like you're being a jerk.
I'm quite sure he did it out of pure emotion and didn't mean anything by it, though. He was probably just incredibly relieved.