Yeah, eventually Apple will allow you the chance for a replacement. Its kinda sketchy to argue for a replacement after just two repairs though, even if it is a pretty major repair. Only after the logic board in my iBook 800 died for the *fourth* time did customer support gladly offer me a replacement. I bet I could have argued it at the third failure, but I was definately told by several customer support reps that two failures isnt quite enough.
Another thing to remember if they ever grant a replacement is their "paid upgrade" option. Basically, they'll credit you back for the laptop (without upgrades) and allow you the option to send them a cashier's check so you could get something else. After four logic board failures I no longer trusted the current iBook line, so I sent Apple a big, fat check to upgrade me to a 15" Powerbook. Although, from what I've heard, those are having their issues as well...
-nick
