This question gets asked a lot, a few folks have had some hard/lagging shifting/transmission issues, BUT that is not particularly common for this car. (some of the strange shifting patterns have been fixed for some with a reprogram at the dealer, I think there was either a technical service bulletin or recall for this some time ago, IIRC, but's it's been quite a while and I don't keep up as regularly with the Y50 platform maintenance since I've got an M37 now.
Cracked, broken dashes seem to be the most contemporary topic lately. The other pricey item is if your auto-leveling headlight motor goes out (can't just replace the motor, it's integrated into the headlight, so you have to buy a whole new headlight)
There are a few more common complaints that seem to come up a little more regularly
may want to search the threads, but to start with:
post6743772.html?hilit=questions#p6743772
post6749064.html?hilit=buying#p6749064
post6631419.html?hilit=buying#p6631419
Two words: pre-purchase inspection...worth every cent
Welcome if you end up buying it and good luck with the search if you don't, these are great cars IMO. You won't be sorry as long as you do your homework and due diligence.
Craig