I hate the pick. I think Hillary is vulnerable to some degree in Virginia but I don't think opinions of Kaine are strong enough here for him to be much of a boon unless they really campaign hard in the state. With campaigning from Kaine they'll surely win the state but I'm concerned they might misread the situation here and focus elsewhere.
Secondly, I anticipate he'll get shredded by Pence in the debate. Kaine is a passive aw shux kind of guy--and while he's a very good guy, he's definitely passive and non-confrontational. Pence is the better speaker with an air of more competency about him despite his awful views, but with coaching it wouldn't take much for him to win a debate against Kaine.
Thirdly, the idea of the importance of the role of the vice presidency actually has gone from one side of the pendulum to the other. We've seen near shadow presidency's in the position before with the likes of Cheney, moderate sage advisors like Biden, to simple figureheads. In the case of a personality like Kaine, he'd be closer to the figurehead side of things imo, and I was hoping for someone that could have greater influence on Clinton.