Ive got one. It works really well as an external gps for a laptop or phone for satnav. Its the same size as the non bluetoooth model. It uses the same firmware too.
We had a BGT-11.
As well as windsurfing, we used in in the car as the GPS receiver for our navigation software.
You can't use the bluetooth to download files (you still use the SD card for that.)
However, you could set it up so that your GPS live-transmits your position via your mobile phone (both in a wetpack) so that someone could track your location. I never actually went so far as to try it out, mind you, but in theory everything is there. The idea of following the blip on google earth was kind of neat.
Unfortunately the BGT-11 is now defunct, but if anyone wants it for the case (for spares) or the bluetooth module, get in touch.
Dylan.