don't have it yet -- but just ordered the Garmin 2730.
why? you get XM, some MP3 (no SD card for expansion though), and the audio output will give you XM or you MP3, and if there's a turn-by-turn GPS instruction -- you'll hear that also.
The big plus for me is that the older 2730 also has an FM transmitter built-in -- so you can get XM, MP3, AND GPS via FM transmitter to your helmet (no wires from the unit to you are required.)
My expected setup? Either a Creative ZEN microphoto (8 gig of mp3) on my body with Etymotic ER6-i or the Shure E3C's earbuds (unit in my pocket, and FM from garmin to to the zen.). If I want the GPS and XM -- just stick the Zen on FM and match the freq. with the Garmin. If I just want the ZEN MP3 -- hit shuffle play (15 hours of Mp3)
The newer 2820 does not have the FM, you have to buy the XM puck, and the Bluetooth is only MONO. so i passed on the 2820's phone ability to have stereo through the FM transmitter.
Now im only struggling with what earbuds to get -- i'll go search for the er6 and e3c