I have a folder under the wallet.dat file called backup.
In that folder I have a symlink to the wallet.dat file and a .bat to create it (if it's missing or to be lazy about it in the future).
I sync the folder with Wuala, thus I have 10 days worth of online encrypted backups accessible on any machine.
It's just the daily wallet, my main wallet is on an Ubuntu machine, it gets backed up into an encrypted archive which gets synchronized similar to the windows one (symlink in subfolder, backup whole folder in Wuala, so I only need to backup 300kb every day, not the whole freaking bitcoin folder).
Yes, symbolic links are cool.