well... just that with bmw's maintenance is quite expensive... and cos there are so many electronics in it... so more things that can go wrong... to be honest i did not have very major problems... and it helped that i purchased a mechanical warranty for the car which paid for almost everything.
I had problems with the automatic windows, leaking gasket, air conditioning, and a few other small things i have forgotten what...
but overall it is a great drivers car! all that power... i saw a 99 m3 coupe with smg transmission for sale the other day which kinda tempted me again...
why are u getting the sedan over the coupe if you want it for a track car?