The caller ID on a BT headset is actually pretty useful. I picked up a Sony Ericsson headset that had caller ID on it. It wasn't a VITAL feature, but yeah, I used to use it with an older, inferior device (Palm Treo). I carried the Treo in my pocket, and it was a bit easier to take the headset off my ear to see whos calling, than to take the Treo out of my pocket.
But I didnt like the sound quality with that headset, so I dont use it any more.
I like the above suggestion of a voice-caller ID, that tells you who's calling. If someone comes out with one of those, I'll be first in line.
Formerly: BB 7105t, T-Mobile SDA, Treo 650, Treo 180,Toshiba e310, Handspring Visor Edge, Casio E10, Palm IIIx, Palm Pilot