Quick update on this so it doesn't fall out of sight, out of mind. There are loads more reports of stolen BMWs on the pistonheads thread which is now 83 pages long which says a lot. However, I still haven't seen anyone post a report of an F series getting stolen in this way which is reassuring - for now at least.
Disgraceful how BMW have denied it's a problem and not provided some sort of free solution to prevent this huge loophole in their security. As someone said in one of the links below, it shouldn't be easier to steal a new £40k BMW than it is a bicycle!
pistonheads thread
Some more info here:
http://www.schneier.com/blog/archive...g_bmws_re.html