Ive heard both sides of the Argument. I think on American cars its a good idea to let them warm up a little since the ones ive owned sound very rough if you just start them and go on 20 degree or less weather. The bimmer so far has not cared either way, and I would imagine by this point these engines are designed not to need to idle, especially with environmental standards the way they are these days.
<img src='http://members.cox.net/inelson5/330i.jpg' border='0' alt='user posted image' />
<img src='http://members.cox.net/inelson5/wooani.gif' border='0' alt='user posted image' /> The whistles go WOOOO!!! *BUBB RUBB FAN CLUB*