Not quite every time, but a lot of the time, after I finish in Windows and boot back into OSX, I lose bluetooth. I even went so far as disabling the bluetooth controller under windows, since I use a wired keyboard and mouse there (gaming with a bluetooth mouse? with all the EM noise in my house? no thanks) and didn't need it. But I /still/ lose bluetooth when I come back into mac. The first time it happened, I was able to get it back by shutting down and rebooting. That hasn't worked today. I've shut down and rebooted twice in a row and no joy. Very irritating.
And, of course, Apple is in the middle of maintenance, so their knowledge base is offline.