Yeah, it will be interesting to watch... and if crime goes down then hey - that's fantastic.
As far as past stats go, they may be perfectly solid. But I dunno... There's a whole lot of factors (economic for one, like Sandman pointed out), and also a whole lotta ways to make stats bend.
So I don't bother with it. Not saying they're wrong... but...
This Washington thing, for me at least, will be a fresh new sort of benchmark. If things go well, all things considered, then the anti-gun guys won't have a leg to stand on.