At work, I use Backup4All to backup changed files from my desktop to the network server, and vice versa every hour. There is a backup system in place to protect the server on a daily basis. I also burn a dvd once a week with the zip files I've created.

At home, I use the same program to copy my desktop to another drive on my home network, maybe once per week. If I were researching today, I probably would make a different decision. The program works, but is just way too complicated to teach anyone else to use. It is automatic if set up right, but it still requires some watching to make sure it's doing it's job.

For off-site, I use Jungle Disk. It's a bit more money but I think it provides more flexibility than Carbonite. However, it's been quite some time since I last researched this, so the features of each have changed, I'm sure. Between four computers, I probably have 60Gb of files stored on-line through Jungle Disk. The first upload took several days, especially on my desktop where I have all my pictures. I still want decent local backups so that the chance of having to get all my data downloaded from Jungle Disk is very slim.

Something I've found is that have a decently flexible backup system still requires too much knowledge to set up correctly to handle all possible failures. Or maybe I'm making it more complicated than it needs to be.

BTW, I've read some good things about Time Machine. If it's able to copy the backups to an entirely different computer and hard drive, then that takes care of a majority of the possible failures. Fire and theft being to two main reasons to make sure you have some sort of additional off-site backup, as you've recognized. Don't forget to protect your computers with a UPS so they have some lightning protection as well.