I just took delivery of my X5 4.8 on Monday and the tranny seems ok. I can feel the downshifts as you slow to a stop but it's not terribly jerky. I don't have any of the lunging issues. I think the tranny holds gears longer going up hills so you'll have power which you wouldn't have if it upshifts going up a hill. My Audi A8 does the same thing on hills.
When I first test drove the X5 in December it definetely lunged starting from a stop. I was told it will "learn" it's way out of it. Obviously they fixed that since mine does not do it. My wife noted how much smother the tranny is on our X5 than it was on the demo car in Dec.
Either the software needs to be updated or the tranny is no good, lunging has nothing to do with a tranny that's learning your driving style nor does very jerky downshifts.

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Porsche 996 Turbo (Ruf 550)
Porsche 993 Cab.
Porsche 997 GT3
Audi A8
BMW X5 4.8 White, Black Napa, Sport, Technology, Premium, Prem. Sound, Cold Weather, Rear Climate, Multi-Contour, Sirius, HD Radio, Running Bds., Bamboo