Impressions are meaningless except for building hype. FB has a small niche, very small. Anyone that has done some serious advertising (I have), knows that quality of traffic counts.
FB will be issuing an IPO soon. They need to because the network will soon collapse under its own weight. Count on it.
There is extreme pressure in corporate America to have a FB presence. Why? Because like lemmings into the sea, everyone else is there so we need to be there too or we might miss something. No one is going to tell their CEO they're not on FB, that's silly. Right? Better safe than sorry. ;)