I would imagine a lot of Googlers have it written in their contract that they aren't supposed to talk about how much money they make. I know most of the companies I've worked for have at least had it in the employee handbook.

Personally, I was okay with divulging that information even when I was working for places that told me not to. I figure if a company is willing to fire or sue me over telling someone else how much they pay me, I wouldn't want to work there anyway. It seems like such a trivial bit of information.