I think renting PC games would almost be impossible. Just think of how many games you have to enter CD keys and make accounts to go online with. Lets take BF2142 for example. The only way I could see them doing it would be if the company who rents the games took the CD key and registered it to a username.... and then sent the username and pass to each person that rented it. But you know as well as I do that the first idiot who got it would be changing the pass and just generally messing it up so no one else can play.
On a different note, I signed up for GameFly a few weeks ago and other than the slow shipping I am pleased. If you have a GF sub you can go to
www.brightspot.tv and watch commercials to earn up to $10 off your GF sub. It does work, I just got my $10 off applied today.