iMac (without network connection) had a date in the year 2000 after rebooting I was having problems with USB devices, so I rebooted my iMac (late 2009 model running OS X 10.7.5). Before rebooting, I turned off wifi. When I logged in again, System Preferences showed the date set to the year 2000. I use the "set date and time automatically" feature, so once I re-enabled wifi, the correct date was set automatically. But shouldn't my iMac retain the date and time? Does this indicate a problem with my machine?
This kind of behaviour may happen when the button cell battery is empty. 

This kind of curious because it should not happen on a machine that ain't so old.