Backup Complete Profile and Save Game Data
path:
dev_hd0:home/0000000x
Each user profile including all save game data is on drive dev_hd0 in the home directory.
With Multiman loaded, the FTP server is enabled by default, or can be enabled in settings. Connect to the PS3 from a PC using an FTP client. You need a good FTP client, one that doesn't stumble up with recursive directories.
Using a USB stick is a better way to back up the profile data.