the problem is related to the PS3 internal hardware clock (not the OS one that you can setup at the options). The hardware thinks that today is Feb 29th but the OS knows that day doesn't exist so it resets itself to 1/1/2000(EUR) or 31/12/1999 (US).
The following models seem to be affected:
CECHAxx (NTSC)
CECHBxx (NTSC)
CECHCxx (PAL)
CECHExx (NTSC)
CECHGxx (NTSC/PAL)
CECHHxx (NTSC/PAL)
CECHJxx (NTSC/PAL)
CECHKxx (NTSC/PAL)
which are most of the fat PS3s. The PS3 Slim isn't affected.
If you haven't turned on your PS3, don't. Wait at least until tomorrow.