In this thread,
http://forum.ppcgeeks.com/showthread.php?t=23129 , a number of us discussed our bluetooth headsets and car kits disconnecting for no particular reason. This problem got worse with successive firmware releases, but I'm pleased to report that two days after installing the leaked 3.49 firmwarte I haven't had a random disconnect in my car. I tried all the other fixes suggested to no avail, but this new firmware seems to be working for me. Hope it works for you too.