Just thought I'd post this email I got, may save someone:
Dear PlayStation(R) Underground Member,
You are scheduled to receive the Holiday 2004 Demo Disc
including the playable Viewtiful Joe 2 - please take note.
It has just been brought to our attention that there is a
glitch in this demo which will erase all of your saved files
from your Memory Card(s). If you have not yet played the
Viewtiful Joe 2 demo, please remove your Memory Card(s)
from your PlayStation(R) 2 computer entertainment system
before you load the Holiday 2004 Demo Disc.
Sony Computer Entertainment America would like to express
our sincerest apologies for any inconvenience this may have