we all have issues
bmw is not as reliable as nissan/toyota/honda. this being said, what tends to go early on e46 cars is relatively obvious and replaceable (control arms)
long term, bmw tends to do poorly on radiators and water pumps (e36 data), but with plenty of warning, and little pissant electrical stuff (window regulators etc).
however: i have not yet driven a japanese car available in the u.s. which can deliver 1% of driving pleasure of a bmw e46. go buy it, it will not dissapoint you.
imho, extended warranty is almost always a waste of money (does not cover what you need covered, and little stuff that goes wrong is amost always chaper out of pocket).