Whenever I start thinking about buying a BMW, I go and check the common problems with the specific engine for the car I'm looking at. So far just reading about their engine problems has scared me off. Same with Porsches, yes they must be amazing when they are working, but so many of their engines seem to have serious mechanical problems. The earlier models that I can afford anyway, couldn't comment on the more recent models.
http://www.bimmerfest.com/forums/sho...d.php?t=852056
BMW diesel engines seem to be a bit more solid, if I really wanted a BMW I would probably get a diesel.