Thanks for your replies / input.

I must say that the bluetooth/GPS interface would be wonderful.

Alas, my el-cheapo Garmin Nuvi 200 isn't bluetooth compatible, so I just turn up the volume to maximum, which is a bit embarrassing at traffic lights when the "Female British English" is shouting "Recalculating ... recalculating ... recalculating". I get lots of stares, and sometimes kids in adjacent cars begin practicing their own English, in unison, in rolling fits of laughter. Definitely not in keeping with my cool biker image.

Another thing that would be very nice is rider to passenger communication - walkie talkies seem kind of silly when the person is hugging your back.

I guess, as suggested, there is not yet a perfect system.

It is very interesting that bluetooth can attain 500M distance - that's considerably more than I expected. The VOX (voice activated) system also seems nice ... however, I have a habit of whistling or singing to myself while riding, so I'd probably be quickly thrown out of the group.