I've had my mid-2007 Core 2 Duo Macbook Pro for just under 4 years and it has needed two logic board replacements, one new keyboard, a superdrive replacement and one new battery in that time. Having said that, all of those were covered 100% under AppleCare and the machine runs pretty much the same as the day I bought it. I would consider myself a pretty heavy user and I take it everywhere so I've been very very pleased with it's longevity.
That's not to say I'm not tempted by the new Sandy Bridge models though...