To my knowledge X3 M Sport production has not started. Speculation elsewhere on Bimmerfest and other online X3 forums is that M Sport Start of Production (SOP) is 4/11/11. If and when it does, I'm sure it will be widely reported. Although I read somewhere that the physiical build is only 2 weeks, something between 4 and 6 weeks from SOP would seem to be realistic turnaround. My dealer is convinced that we will see our X3 around mid-May. That feels aggressive to me, but I've developed lower expectations given the months and months it's taken to see my various M5s arrive from Germany. My last one, which was the first one delivered in Oregon, was ordered in early August and arrived in late November.
One other bit of news from my dealer, apparently the availability of the mechanics or the electronics for the power rear door feature have delayed other X3s they have on order. Since my wife is coming off a Lexus RX-400h and adores this feature, we'll just have to wait that one out as well. She waited two years to get her RX, so she's also not in any hurry on her X3.