I took a quick test drive of a metallic silver 2008 Porsche Cayman, 5MT, red leather interior. $50,000.

Exterior:
It's quite beautiful to look at. It has a popup spoiler which operates in a manner similar to the Carerra GT. The curves are great.

Interior:
Very well made, soft plastic dash, leather on the doors, seats, and center console is very nice. The climate control system is very, very impressive. Set the temperature and forget it. Selection of footwell, front, and dash blowers can be done individually. Very straightforward and simple. Storage containers in the arm rests as well as behind the driver on the sides. Surprisingly roomy front trunk as well as rear trunk. Visibility is much better around the front, sides, and rear. The hood slopes down in the front, so you can see quite a bit. No blind spots.

Maintenance:
That engine looks like it would be a pain in the a$$ to maintain. Maybe drop it out of the bottom of the car like the 911's? Oil, coolant, windshield wiper fluid can be filled/checked fairly easily however.

Noise:
The Cayman is noisy on the inside and there is a metallic "whine" to the engine when revving. Not anything like the dead silence of my XF. The exhaust noise stock is drowned out by the odd noise of the engine revving. It's fairly quiet for a mid-engined car, but it's a little disconcerting to hear engine noise instead of the exhaust.

Driving "feel":
Steering is tight and responsive. The car corners fairly flat and at very high speeds. The steering doesn't feel any different from the Crossfire, but the car feels much lighter at the front than the XF and definitely understeers less around high speed corners. The Cayman definitely rolls much less than the base XF and feels more secure at the limit. The suspension feels very well tuned stock and doesn't jolt going over bumps. 1st and 2nd gear are "high" meaning that acceleration is fairly weak down low.

The shifter doesn't feel any better than the XF, in fact it feels a little softer and not quite as precise - almost like it's using a high quality cable shifter instead of linkages. It's strange that the Caymans only came with 5MT's until MY 2009.

The steering wheel has 4-way adjustability and is fairly small, which is nice.

Practicality:
The inside is very, very tight. It feels about as small as the Honda S2000 in the interior, which means that if you are taller than 6', then you won't fit comfortably in the car. The 911 is a much larger car on the inside than the Cayman.

Power:
At 265hp, it feels weaker than the base Crossfire. In fact, the Crossfire blows the Cayman away in first and second gear, and the XF feels like it has much more torque down low. I think that the extra 1000 revs on the Cayman engine gives it the 50 hp up top.

Conclusion:
Is the Cayman worth $50k or more? I don't think so. I think the average Cayman buyer would be better off paying the extra money for a base 911. That's what I would do. The 911 gives you rear seats and more interior room.

That said, I would definitely buy a Cayman over an Audi TT or a Z4 - no contest.

Notes:

On the test drive, I passed by someone driving a Crossfire convertible going north on 395 in Washington DC. The XF is lovely.

After driving the Cayman, I can definitely see that the Crossfire's tires are totally out of whack stock. 225's in the front of a car with roughly 60-40 weight distribution is strange. It makes no sense. It's like somebody from marketing said, "People want fat rear tires on a car that's RWD." and completely ignored a hundred years of automotive design fundamentals.

I want to mount 255's or even wider on the front of the XF.