I recently purchased a Motorola MOTOROKR T505 to enable bluetooth in my car (Honda Civic Hybrid). I previously used a connector for my phone that let me connect power and a headphone jack to the car. The audio went to an auxillary jack that was built in to the car. There are a couple of downsides for this. There are a bunch of wires all over the place making the care look a little messy and when I talked to people with the power plugged in, they heard loud static and "screaching".
So when my Android phone got the new cupcake update that had stereo bluetooth, I wanted one of these fancy blue toot car sets that would let me just hop in my car, hit play on my phone, and head off down the road. If only it had worked so well. The first issue is that one of the things it says in the manual is that the T505 was not designed to stay in a hot car all day. I don't know who didn't put that requirement in, but I already carry a big phone around, I'm not going carry around this garage door opener sized thing with me too. It also ran on battery so that would eventually run out and I'd have to plug it in to the provided charger. I just left the thing plugged in so I wouldn't have to worry about it running out of battery at some unfortunate time. This mean that I really couldn't have it on my sunvisor though without having a power cord dangling around. The next downside was pretty annoying, when I got in the car, it was a lot more than just hitting play on my phone and driving down the road. I had to get in, turn on the T505, wait for it to turn on, hit the FM button, (meanwhile listening to my car spew static from the station the T505 is supposed to broadcast to), hope that I didn't accidently hit the FM button twice because then the T505 would go find another station to broadcast on, wait for the blue tooth to sync with my phone, then finally hit play and go.
This was all really too much for me. I brought the T505 back to Best Buy and got a refund. I will try out some other connectors for my wired solution that hopefully don't require me to unplug the power when I talk on the phone.