Yea, michaelochurch have talked about "open allocation" before.
I don't know if this is common now or only applies to people coming off of the industry track instead of the university track, but it was not at all what I'd been warned to expect.
So far everything about Google has been generally fantastic. I'm hoping it lives up to it once I'm inside.
I do suspect it has something to do with your employee bargaining power, which depends both on your past track record and on how many people are being hired relative to staffing needs. Managers bid on Nooglers, draft-style; if many teams are bidding on you, you have a lot of flexibility in where you end up, while if only one team bids you're basically stuck with them. michaelochurch was hired in 2011 IIRC, when Google notoriously overhired, and it could be that many of the other teams were flush with Nooglers and not looking for anyone else.
Just my experience; I started at the beginning of 2012.