I'm still looking forward to the Dension solution (end of June according to their website for E90/E91 and other new BMW's).
Assuming the integration aspects are the same [perhaps a big assumption] the dension solution gives you the ability to plug in USB devices. I haven't looked around but I'm hoping there's a nice fat USB hard drive - maybe updatable via WiFi! Then I can keep my music collection in sync whenever the car is near
that would be very cool