'Ere, someone's been through and cleared away what could have been a very entertaining afternoon :-(
Anyway, Aeronut, you've had a few opinions by now so my tuppence is, go for whatever method you feel happy with, as long as you make sure backups are part of the scheme. Since most people give up on backups at some point, I'd consider giving over one 320GB as a backup of the other. As SD says, you could RAID1 the drives. But, if the computer is trashed along with one of the RAIDed drives, you need to know that the data on the other drive is truly recoverable. I wouldn't use RAID 0, because "0" is the amount of data you'll recover if things go pear-shaped. This is down to your skill level and possibly the availability of replacement hardware. What I'd possibly do, in my specific situation, which includes being in an earthquake zone: an external drive as a real-time backup target using something like Comodo Backup, which is free. If push comes to shove, the drive gets ripped from the cable and stuffed in the egress backpack. Of course, my needs are probably different to yours :-) I just need my business paperwork and my photos to survive. If you look carefully at what you really, really need to survive the ultimate disaster, maybe a USB stick would would for you.
The main thing is, choose a system you're comfortable with, and which works without your input.