If it's wrong, it's not far off. I run some Facebook RPGs. I did an estimate using their user numbers (not hard find since the networks publish them) and assuming similar revenue per user (RPU) to our games and guesstimated $75m. Their games probably also have higher RPU than ours, so I could totally see $100m or even significantly more now that FarmVille is taking off.

On the other hand, as MixPanel pointed out, they buy a LOT of traffic. Not just on Myspace either. On both networks you can build a compelling enough game to get your RPU above the cost of buying a user. The difference between the two is that on Facebook, your app can succeed without that.

Zynga's spending what has to be at least $2m/mo in ads, maybe 3 or 4. They're also using ads on their games to cross promote with other games, and those ads could be bringing in money too. When you factor that in, as high as 50% of their revenue could be going right out the door to advertising. (I don't think that's the case though, if I had to venture a guess I'd say 20-25%).