I don't mind them so much in stuff like footie and racing games because it fits in with the theme of the game, but something like fallout 3 would look a bit weird if it had today's adverts in it. This also brings up another possible problem, what if advertising revenue became quite big and the game companies started making lots of money of it, it could potentially influence future game development, think of a scenario were a publishing company is going to fund 1 game and 2 people turn up to pitch a game.
Game 1 is 'Toon Army - Battle back from relegation' a generic footie game, nice and easy to put loads of adverts in the problem is that it's a bit naff.
Game 2 is 'Funky Space Monkey' - space game set in the year 3000. Hmmm, bit more difficult to keep the ads relative, the problem is the game is mint.
It would be a shame to see games start getting the green light just because they are easy to fit the adverts in, and see them squeeze out some other types of games that maybe are more difficult to do advertising in.
As for adverts at the start of games, just a personal thing but I would hate it and if they made it so you couldn't skip it I'd probably not buy the game, I know that sounds daft but it's one of those things that annoys me, I already go nuts when I fireup a 360 game and have to sit through 10 different developer logo screens, if they started putting ads on it would drive me insane.