Just discovered this thread and, while I don't have the 2008 E90 6MT anymore (replaced by a 2011 E90 DCT recently), I used to wonder about the notchy, grinding shifts from 1st to 2nd. But, whereas the majority of people seem to experience it when shifting at high RPM, mine used to do it at low RPM shifts. Each high RPM 1-2 shifts were fantastically smooth each & every time, but shifts at low RPM would often result in slight grinds & notchiness. Didn't even bother asking the SA or mechanics at the dealer where I got it from as they've proved themselves to be a bunch of incompetent numbnuts.
On a different, but possibly converse note, when I upshift (any gears) DCT at full throttle/redline, I hear a thunk and substantial movement under the car. This being my first DCT/SMG car, it's unexpected and I had imagined that that's how SMG is, and therefore, expected DCT to be totally smooth at redline upshifts...