You mean like the NVidea logos that have played at the start of games for around a decade now?
I draw the line at the point it doesn't make sense within a particular game - they can put all the ads they want in Deus ex as its a near future game with tons of fictional advertising in it anyway - they may as well make a bit of money on the side. If they were doing the same thing, in say, Dragon Age, I'd have a lot more of an issue with it as it wouldn't make sense within the context. The second line is when advertising interupts the actual gameplay experience - if it say pauses at a loading screen to try and sell me coke, that would be too far. But for small logos in the corners in a game that would have advertising around, I really don't mind whatsoever.
I'd much rather reward a developer with my money for making a good game than not buy the product and contribute to a developer going down on the basis of somethign that has nothing to do with the game itself. Good game + ads is infinitly preferable to no game at all.