There are certainly still a lot of questions around the USB interface.
As the AUX interface is basically only an AUDIO input, the USB interface is only a DATA reader, hence the player is in the Idrive. From an operating point of view this USB option is a lot better as it integrates with Idrive and you can feed any data type (MP3 player independant).

But as ozx5 says, there are still many questions unanswered and no dealer knows. I've also ordered it with the expectation I can connect my USB harddrive to it..

This would be my list of questions around it:
- What formats supported? (would I need to convert my audiocollection from WMA9?)
- Having 3200 songs on my drive, would it handle that?
- Would it support album/genre/artist listings and playlists? (like a real media player?)
- Will it power my USB Harddrive, and will it powerdown when I remove the keys from the car?
- Will it still be fast enough with more than 3000 songs, or will it completely become unusable (slow) as it was not designed to hold so many songs.
- And all the questions from ozx5 about display info

The first cars with this options should now be on the market as production started in April, as soon as my dealer has one, I will test the above options in the showroom. Will post the results here if noone has done so already in the meantime.