In all honesty, I don't think Google would do much to try and control Valve. We've seen Youtube post Google buyout, and not much is different over there. The one thing I think would change, is that Valve would have a lot more money at their disposal, as well as a wealth of new internet resources to be able to get a hold of. I think that's why this would be a good thing for us gamers, as well as both Valve and Google.

Yep, I kinda agree with this. I can't imagine Google would go after Valve with the intention of majorly shaking things up afterward.

AFAIK, Google aren't pure evil yet, so, like you said about YouTube, I don't think the impact would be negative.