Lots of opinions - I think it's generally not advised, but if it's not winter and your not racing around all the time you might be ok.
Search on google - "mixing RFTs"
http://www.z4-forum.com/forum/viewtopic.php?f=2&p=222967
http://www.pistonheads.com/gassing/topic.asp?h=0&t=1000084&mid=0&nmt=Mixing+runflats+and+standard+tyres
http://forums.overclockers.co.uk/showthread.php?t=17960922
http://www.bmwland.co.uk/forums/viewtopic.php?f=1&t=115028