"Does anyone have any experience or opinion of these cars? Any warnings?"
a good friend bought one... pretty sweet when everything working. I dont know much but here goes.
Make sure you get a PPI and check the usual stuff.
(shocks, load level suspension ext)
the only real problems hes had are replacement of the computer when it took a dump$$$ and thust arm bushings?(i think... thrust arm something) He was told the rubber boots on the ITB's can crack and let one cyl go lean an wreck the motor(which i hear isnt cheap to rebuild)
If you dont care about the badge or its a second car. consider a 535I.
I convinced my friend to to a dyno day with a few PNW guys too..
the results are in this thread.
http://forums.pelicanparts.com/showthread.php?threadid=263258&perpage=40&pagenumber=2
EDIT: i forgot: REALLY tiny rear brakes... like... 518i -ish