A long time ago I bought a MS bluetooth mouse, which comes with its own dongle. It cost €99 I think, which was the same price as a bluetooth PC card. I thought I was getting a deal but no, the MS dongle is slightly different etc. etc. and would not work with my phone (a Nokia). In the end I bought a generic bluetooth pc card for about £40 and uninstalled the MS bluetooth stack, now all is lovely, the phone connects and does all sorts, the mouse still works etc. I still have some niggles with my carkit, but I think that is mainly because the stereo "ducks" if there is any change in status of the phone or the bluetooth link. If I leave it in the door of the car, no problems though.
As for headsets, I have linked my Nokia HDW-3 to my laptop and can use it as a headset BUT it must be disconnected from the phone first. After I discovered this it took all of 10 seconds to get it sorted out with messenger etc.
And as for Macs, my ex-girlfriend bought one of those shiny tea tray laptops, and never got any joy out of the bluetooth (it was an "old" one though, she bought it about 18 months ago).