Windows 7, iTunes, and the iPhone
If you are an iPhone user, be careful about syncing your iPhone from a Windows 7 computer. One of my friends installed Windows 7 RC (release candidate) on his computer (from scratch) and then started using iTunes and syncing his iPhone. His Bluetooth headset stopped working. When he tried to enable bluetooth, the icon would just spin, but it would never enable. He tried resetting the device, turning airplane mode on/off multiple times, and more.
He finally took it in to the Apple Store and they said that Windows 7 was not compatibile with the iPhone should not be used. They had to completely erase the iPhone and reload the firmware. But, once they did, Bluetooth started working. As soon as he took it home and sync'ed it again, Bluetooth stopped working again.
Finally, he had to wipe the device out completely re-install the firmware again. Then, he sync'ed it from a Windows XP computer and Bluetooth has worked ever since.
I'm assuming this is a problem with iTunes that will be fixed as more people report this.