I found this article on the same topic. Link
This article adds that installation would cost $149 in addition to the $149 price of the adapter.
In my opinion I'd rather spend $300 toward a new head unit that has a much better display of the MP3 tag information.
The part I find encouraging is that BMW is acknowledging that portable players have a place in the car. I would think that BMW will eventually offer MP3 capable CD players and a much better display for the tag info plus an easy connection to a portable if you have one.