Have been going through same thought process and have decided to not wait for F15:
1) Have same concern as others about first year of new model
2) I don't necessarily want a larger SUV
3) BMW often changes hub size on new models so that my current winter rims and tires may not fit on F15
4) Last, but not least, not having at least a space saver spare is a deal breaker for me and there is no assurance that the F15 will have one.
So placing an order for 2013 35d configured identically to my 2010 except for color Platinum Gray( don't like new bronze color, too brown), and going to upgrade to Enhance Personal Sound, option 752.
2013 X5 35d
2012 328i Wagon
2010 X5 35d (Retired)
2008 535xi (Retired)
2005 X5 4.8is (Retired)
2003 M5 (Retired)
1999 540i (Retired)
1987 325i (Retired)
1973 2002tii (Retired)