That wouldn't work on a well protected system. A system that is vulnerable would be protected by OSX's security system called File Vault. Each user's files are encrypted and for every user the encryption is different (it's encrypted through the password.) Not even root can access these files, and when Leopard comes out everything will be backed up on a separate hard drive by Time Machine.

OSX is open source, if there was a vulnerability, one of the hard core geeks would have found it and offered a fix, just like Linux.