I've seen a number of mentions today of a bug that can cause a Snow Leopard user to lose all their data:
One user reports a way to recover the lost data. Since it's buried in a discussion thread, I'm reproducing it here (also fixing a typo pointed out by a reader of this blog):
The problem appears to manifest itself on machines which had the Guest account option enabled under Leopard and were subsequently upgraded to Snow Leopard. Users booting their machines have reported that upon start-up, they have been logged into the Guest account. Upon switching to their regular account, the affected users have been finding all of their user data missing and unrecoverable except from a backup. [MacRumors.]
The files were still in /Users,
recovery was not too difficult.
1) su in terminal
2) mv username username.old
3) create account username
4) mv username username.new
5) mv username.old username
6) chown -R username username
I don't know whether it's a general fix. If you run into the bug and decide to try this solution, feel free to post your experience in the comments section!