This has happened about 6-7 times now in the last two weeks. Ran a quick and extended Apple hardware test on it and both came back fine. Also, changed the power outlet it was plugged into and still is happening randomly.
Wirelessly posted (iPhone : Mozilla/5.0 (iPhone; U; CPU iPhone OS 3_1 like Mac OS X; en-us) AppleWebKit/528.18 (KHTML, like Gecko) Version/4.0 Mobile/7C144 Safari/528.16)
Power supply unit my 2006 iMac started this a few weeks ago as well shortly after I installed
snow leopard. It hasn't done it in days though