...the Cayenne is as much a real off-roader as the X5 or ML are. I'm sure it is capable of a nice off-road performance but an old Landcruiser or a Landrover would be worlds ahead when it comes to real off-roading. But that's not the point.
You're right, the Cayenne will stay mainly on the street. So why does Porsche try to point out it's off-road capabilities?
My personal guess is that they want to distract from the missing sportscar capabilities. When first rumors of the Cayenne appeared about two years ago, everybody was thinking that Porsche will invent a new form of SUV, an off-road sportscar, one of it's kind. Now that the Cayenne is available, people realize that a 2.4 t SUV can't be a sportscar, so Porsche tries to convince buyers by the Cayenne's off-road capabilities. I wonder who takes a 90000 $ SUV off-road when he can have a highly competitive off-roader for less than half of the money.

There is also another strange thing: the VW Touareg has been already tested in several german car magazines. The Cayenne not. Strange or not ?! We're still working on our Cayenne testride report and I have to confess that it isn't easy at all. We don't want the Cayenne to look bad but we don't want to make it the perfect SUV because it isn't.

Regarding to the on-road capabilities, I can provide some short points of referral:
1. the Cayenne Turbo is way too heavy
2. the steering is great and provides a much more direct feel than on the ML for example
3. the automatic tranny reacts too slow, especially from standstill
4. the engine/exhaust sound isn't spectacular at all, the ML55 sounds "meaner"
5. the handling capabilities are great, you don't really feel the weight
6. interior/exterior build quality is impressive (to Porsche standards)
7. the trunk (or loading area) isn't as big as on the ML, quite a disappointment
8. rear passengers have much more space (especially for their feet) than on the ML for example but I'd love to see less rear compartment space and more luggage room
9. fuel consumption is extremely high, couldn't get it below 29 l / 100 km (my 996 Turbo takes around 21 l / 100 km...maximum)

Overall, the Cayenne Turbo is a great SUV but too heavy, overpriced and it eats too much fuel. I'm not sure if Porsche can maintain the predicted high sale figures for the next few years.