I was given a preference sheet to fill out after receiving an offer, and I was given my first choice, also. It seems there is quite a bit of leeway to change teams if one finds something else more interesting.
I was kind of bored in my current job, and Google contacted me to interview.
At first I was hesitant because of my failure the first two times I interviewed and the fact that I now have a house far from the office. Both times before, I thought I had actually done very good.
I decided to go through the process, though, because I would really like to work at Google all things being equal. In the end they offered me much better compensation and stock than my current job. However, my company countered with a new role, more money, and options.
In the end, I have decided to take the Google offer and at least try it.