Scott,
I highly recommend Carbonite. As you know part of my day job has me responsible for the well being of 50 computers and the network that goes along with it. For 2 users who are working with very sensitive financial data I use Carbonite to back their files. It works seamlessly, everytime they add or change a file it's done on Carbonite in the background.
Yes backing 750 gigs to Carbonite will take days. In the case of the firm I work for the files are realtively small, mostly spreadsheets and Word documents. I had been using Carbonite at home for a couple of years because it was provided as a free service from Cox Cable my former ISP. I've since moved to Verizon using their Fios service................which leads me to backing up on my data on 3 separate external drives. I keep one at home, one at my office in a fireproof file cabinet and one in my briefcase.
Fran's suggestion is a good one, but imho you have nothing to worry about with Carbonite being insecure. The downside long time to upload files, then if you have to restore the files it will also be a time consuming process i.e. if you had to restore all at once.
And just playing the devil's advocate, your files are constantly changing. Do you want to make a visit to a safety deposit box at your bank to update files? Something to think about.
One other thing about Carbonite, it's a no brainer for my users and more so for me. I never have to worry about them having remember to back up sensitive files that change. If they were to lose any of that financial data, it could cripple the firm and possibly put it on the brink of going out of business. Of course other systems in the firm are backed up to tapes and stored in secure locations as well. Redundancy all the way.
[This message has been edited by Stephenm52 (edited 01-11-2010).]