This is my first post as I am picking up my 135i in a few hours. It seems appropriate that I comment on the car that I just sold. All in all the 996 is a great car except for one very serious flaw. It has the M96 engine that is susceptible to catastrophic intermediate shaft bearing failure. Take a look at:
http://www.lnengineering.com/ims.html
The IMS gave Porsche so much trouble and they have had to replace so many engines that in 2008 the redesigned the motor without and IMS altogether. Engine failures are so common that most dealers stock at least one complete replacement motor.
Edit: I should add that Porsche used completely different engine on the Turbo and GT3 versions of the 996. That motor still used the older 964 block. The Turbos and GT3's are great fantastic cars with very strong engines.