Just to expand on my previously mentioned pessimism - is anybody worried about security? I would be reluctant to upload much of anything - eg photos, personal info, financial stuff, etc, without some serious encryption. And that's just another level of PITA.
Mozy has built-in client-side encryption. Whether that's actually credibly secure protocol and implementation of the 448-bit Blowfish cipher (practically unbreakable on paper) used is impossible to gauge since they don't publish the source code or protocol (protocol is usually the weakest link, not the cipher itself).
The only way to be sure is to backup up encrypted files to your own server, as I'm confident none of the services allow any level of security auditing of their encryption protocol, and almost as confident that all of them have vulnerabilities or backdoors.