If I try turning Bluetooth off, then on again before a soft reset, the phone hangs at the "turn Bluetooth on?" query screen and doesn't turn it back on. After a reboot, everything's fine till it fails again. It's not my data connection, because I can still browse the web from my phone.
dartinbout in the eXpo users' group seems to have been having similar problems with his stereo Bluetooth headset.
I also seem to recall having similar problems with WMWifiRouter as well, but I can't test it anymore as my trial period has run out.