I've been using Mozy Online Backup for the last year so far and have been satisfied with it's easy to use and configure interface. I'm currently using the 2GB free service they offer and have had only one minor issue so far.
I recently had to do an online restore for files I had backed up and ran into one problem. Mozy encrypts your data for security when it is saved on their backup servers. Any data you retrieve for restoration, is still in it's encrypted format.
There is a Decryption utility that needs to be used before decrypting any data for use. I noticed that their decrypting utility was a dead link on their site, so I had to email support to retrieve it.
The link for the decryption utility is:
Apparently the link is broken on the "free" Mozy side of the web site........hopefully this will be fixed shortly.
Other than this minor issue, Mozy seems to be good choice for free Online backup.