I freaked out a little a few hours ago because my iMac hanged. After forcing it to turn off and rebooted, for whatever reason it didn’t recognize its own bluetooth transmitter (no bluetooth detected in system profiler). I thought crap, the BT transmitter is dead or something. I searched google, and found out about users resetting their SMC. Apple has this document: http://support.apple.com/kb/HT1543 I followed the instruction and my iMac is back to normal. Phew. I was afraid I had to restore a time machine backup, or worse, hardware failure.
iMac acting up