Sorry to hear about the data loss.
I lost my first set of digital photos back in 2002, after that started a much better backup procedure. From my experience backing up is a balance between fault tolerance and price. It's like the old saying, "data recovery, speed, cheap, pick two".
Based upon the idea that you have two systems which need to be backed up I would recommend the following.
1) Set up a folder for all of your images and make sure that nothing else you want backed up is placed in another directory. I'm not familiar with Mac, but you could create a folder structure like /home/user/images where this would be all of your images.
2) Create a cron job to backup the /home/user/images folder to another local directory or drive. Another drive would be best but on the same drive would be ok for now. The idea here is to guard against any accidental deletion of the entire directory.
3) Create another cron job or script to copy the /home/user/images folder to a USB device. Also when you copy the files, use a utility that verifies that all of the images have been copied over. I think you can use the command diff to compare two directories, in Windows there is a tool called Robocopy that is great for this, scans GB of data and shows the different files in seconds, assume there's a tool in Mac.
4) Install a cloud backup agent. You can use Mozy or any other vendor like Jungle Disk, but stick with a larger company. Now this is not a 100% backup since it's going to the cloud, but it's just another layer of backups, also it's cheap, I think I pay $10 for two systems on Mozy.
5) Hard copy backups, once a month (or quarter) export your latest files to DVD for archival backups. This is going to be a huge pain the first time but after should be much easier. I know people will say "DVD's are too small 4.7GB is less than one card" but my reason is it's the most readable format possible. Do not use a backup software to create these disks unless you are certain that 10~20 years from now the software company will still be in business. These archival backups should be kept off site, like an in-laws house, bank deposit box, local storage locker, etc. Do not keep the archival files at home, next to your computer.
6) Test your backup procedure monthly. Make sure that you're backup procedure is tested and working. Login to the cloud backup software, retrive a file or directory. Try calling back some of the DVD's you made, can you pull data from it using a Mac or PC?
I like to build simple solutions over complex, I also follow this same path at work managing data backups for a small data center. This reason, I do not recommend a RAID SAN or NAS in place for a home environment unless you calculate the extra time and effort required to monitor the device. Each added solution to backup is like adding another link to the chain, it's another possible fault and another piece you need to check. I like to keep the chain as short as possible, this way you don't become lazy and forgot while you assume that the device is doing it's work.
Now, if you really have the time and effect, throwing a NAS in RAID 5 with a few TB of data would be nice to add after step 5. I haven't used home based NAS or SAN devices but I think they might offer some reporting tools, if a drive has failed send you a e-mail, or maybe even a phone home reporting so you'll get a call from the vendor with a replacement drive.
Basically, you want multiple levels of backup. Don't trust one method 100% as it may fail, and you never know when the worst will happen.
Good luck!
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