Can't give a proper review until I've spent some more time behind the wheel, however first impressions are superb. Initially I was torn between the Cayman S and the Z4MC, but was put off getting another Z4 as I thought I would get bored very quickly, so the Cayman was the front runner. However I preferred the looks of the Coupe and thought the interior of the Cayman let it down. Both are excellent to drive, though the extra power in the Z4 is noticeable, it certainly feels quick, just as quick as some of the higher powered cars I've driven (although I know it’s more the sense of speed).
If you're interested in buying one, now is an excellent time to do so. Mine is four months old, done 5K miles and has lost 14K!

Will take some more pics tomorrow.