Friend of mine has the nokia kit, not that great really, have to shout to be heard and the microphone is mounted where it should be. I used a parrot kit for a while, seemed a decent bit of kit but only used it a couple of times so didnt really get a proper evaluation of it.

My car has got factory fit bluetooth, is bloody awesome, voice control through the phone's phone book etc. Definately get what you pay for IMO.