i saw infernal affairs a couple of years ago at my college's international film festival, and i have to say that i found the concept of the flick a bit too convenient. i know it's supposed to be a thriller and so it doesn't have to strictly adhere to my concept of reality, but for one reason or another i thought the idea that there was a criminal in with the cops and a cop in with the criminals was a bit too cutesy.
for what it's worth, though, i have no problems believing the general plotline of something like die hard, which is--all things considered--probably less likely to happen. so maybe i'm misguided, but infernal affairs and the departed's plots just did next to nothing for me.