 I've had my Z4 for about a month now. 
Got all the options - Performance & 
Sport packages, Steptronic, heated 
seats.  A little pricy, but lots of 
fun.  The car drives extremely well and 
will behave as reserved as you want it 
to when in normal mode, but transforms 
into a real tiger when you push the 
Sports button or shift the Steptronic 
into sports drive.  There is no 
comparison to the 2.5, which felt 
underpowered.  It is a little bumpy 
with the 18" wheels, but not as bad as 
I had feared.  Watch out for pot 
holes!  It does not handle puddles very 
well (easily hydroplanes).  It is a 
real eye-turner for young and old 
alike.  