Over at
Mercedes-Benz.tv | english - The IPTV of Mercedes-Benz they are showing some footage of the new SL with the head unit that takes SD-flash cards and they talk about the new USB interface for all devices.
A new menu appears called "media interface".
You can basically assume that by the end of 2008 there will be so many options that you wont know which to choose from. Maybe too late for some but worth keeping in mind.