I've had a few relatives that owned BMW's, and they all had failures of some sort. My favorite failure was the one time that the driver's seat just started reclining back while my uncle was driving, and it wouldn't come back up. Cost him about $1000 or so to fix. This was in the mid 90's, so maybe BMW quality has gotten better since.

That said, I think the BMW is probably more of a driver's car than the IS.