First, Excellent question. Although this is an obvious query for a prospective owner, it is rarely asked.
I have mixed feelings after 40K miles. I love the way it looks especially in Blue. Love the Wheels. I love the way even with its mass and weight it can still explode from a stand still when your settings are right. I like the way the interior is put together and arranged. I like the Heads Up Display. I like the amount of carrying space.

I started out liking the iDrive but now I find it too slow. Without M Mode engaged the car feels a little ponderous. With M and Sport on, the car feels dangerous in a good way. But its acceleration and speed do not feel effortless. Some may like this, but over the past 2 years I have come to want the same acceleration but with more stealth. The sound system in its most upgraded form, is lacking in terms of clarity, power and bass response.
That's all that occurs to me at the moment. Have had to bring to the Dealer a few times for a turbo hose, a climate control issue, and squeaky brakes, but nothing excessive.
Would I have done it again? Oh yes. Best bang for the buck in late '09 by far!
Would I do it now? Probably not. Porsche has really improved the Cayenne, and I've been saving up just in case.