Can't give you figures, partly for the reason Jazzee mentioned, partly because AltyFC would kill me and partly because he gets the cheques so I'm not sure...
A lot of the earning power of it depends on what sort of site you've got and the number of new visitors coming to that site. For example a site like AardvarkTravel (see sig) which has lots of unique visitors does probably a lot better than say this forum might because once people have seen the ads they are more likely to block them out.
As for amounts earned per ad - impossible to say as you'd have to know how much each advert was costing to work it out....something Google ain't going to tell you.
If you're thinking of doing it, why not just put it on and see.
Trev