I get 400 full resolution images on my 1GB CF card with a 5 megapixel camera. Now you can get 2GB cards for the same price as I paid for the 1GB. 2x1GB cards are only a couple of dollars more than a single 2GB card so I am collecting them instead.
By summer (southern hemisphere) I will have 4x1gb cards, enough for a week spending more time taking photos than riding, even if I upgrade the camera to one that writes bigger files. I have never had a glitch with CF cards but I figure, why have all your eggs on one flashcard?
On the other hand, as an IT technician, I go through 2-3 portable hard drives a year due to wear, tear and getting knocked around. The photo tanks like you have look neat for extended touring, but I wouldn't trust them more than solid state. Get a pelican case for this gizmo.