My friend just bought the dealers Demo 335 vert. (It had ~4-5K miles on it.)
He's had it for about a month and has already had to take it back to the dealer for repairs a couple of times.
Everyone I've seen take out the demo M3 beats the SH*T out of the car. 2K of MSRP in not worth it.
My friend got the 335i demo at dealer cost and some freebies (ipod adapter etc) He got his car for about 5k+ of MSRP on a car that is 20K less than the M3