And now the problem is that files with "," or spaces in the name fail... The "reversible scrambling" proposal above might work (though not ROT13) - that way the data is there _if needed_, but it takes concious effort to take a look.

If in the process of debugging the "," issue, a set of files is uncovered (including "how to file a divorce", tough. Ideally, the usernames could be unscrambled separately, so at least there's no immediate connection to a single user.