We just bought a 2007 XC90. We followed our Volvo mechanic's recommendations as to which is most reliable. He told us 2006 and up are the ones to get and the most reliable package is the FWD 3.2l six. So that's what we got. He says there's nothing wrong with the AWD or the 2.5l turbo, but just that they are more complex and thus require more attention. He told us to stay away from 2004 and 2005 models, said they have a GM tranny that has issues that apparently can't be entirely corrected. Sorry I don't have any more specific info than that. But you're good cuz you're looking at a 2006.

I guess the only other thing I'd suggest you look out for is rust and/or corrosion, especially if you live in a state where they put salt down on the roads during the winter.