I drove an SMG-equipped 650i once, and did not like the SMG. My time in it was very brief however. The impression I came away with was "if I'm going to jerk my passengers heads around like that, I might as well be shifting myself."
However, I really want to get SMG on the M3. What I REALLY want to know from current SMG owners is this: Can you develop a technique for smoothing out the shifts with SMG? i.e. lift off the throttle a bit before the shift? I know I can shift a manual myself perfectly smooth, without any jerking. It's just a matter of speed with my hand and correct timing with the pedals. At least it's possible.
Is it possible to get a perfectly smooth, seamless, almost "automatic-like" shift with SMG? And what does that require?