It took a lot of research and consideration* but I finally made my choice: I'm using MozyHome as my personal off-site backup service. I paid in advance for a year of unlimited backup space, downloaded and installed their software, and began configuration. There was only one moment when things didn't look good… an error message appeared saying the service couldn't connect with Mozy's servers. Clicking on a link within the message box, however, took me to a Web page at Mozy that indicated it was probably a firewall issue on my PC. A quick edit to the XP firewall, the configuration connection was established, and I was in business. Using their "Advanced" configuration option, I selected a few important directories on my PC, clicked on the [Backup Now] button, and it began. Less than half an hour from purchase to first run. This morning I checked on my computer and a message box on the screen told me the backup had finished successfully. Before I headed off to work I selected several larger directories (mostly photographs) and began another backup. So far I'm liking what I'm seeing and it will be reassuring to have the service in place when, next week, I begin my big annual publishing project.
PhotonStopper 
I recommend IDrive (www.idrive.com) for online backup. One thing users need to understand about "unlimited" backup offers like Mozy is that there's always a catch… most often, the speeds at which you can backup your data are artificially capped or limited, so backups take longer. IDrive can utilize the full speed of your broadband connection and has been proven to be significantly faster, incredibly reliable and quite popular. You can get a 2GB subscription for FREE or get 150GB for $4.95/mo (or $49.50/yr).Robert HainesBusiness Development Manager – IDrive
Thanks, Robert. Unfortunately I was looking only at the highest-ranked online backup services in several reviews and even that was a daunting task. Had I known the details of IDrive I may very well have gone with your service. Oddly, however, for such an important feature as higher data transfer rates, I can't seem to find reference to it on IDrive's Web site! Certainly I don't like paying extra for faster data transfer since I'm already paying my ISP for broadband. I have, however, already paid my $50 to Mozy for a year in advance. Mozy's a good service, so far as I can tell, but S-L-O-W (as, apparently, are most online services) unless you sign up for Mozy's "Pro" plan which would cost me way more than $50 per year. Perhaps I'll shop around again in 2010…..