Hyperdrives work pretty well. I have the HD80 which has the advantage of working on AA's. Functions as both a drive and a AA charger for my flash (although slow). But the backup portion of it works great and is pretty fast.

As for buying more cards: I personally only like using the top quality brands (Sandisk Extreme) which are still pretty expensive. If you're shotting RAW, cards fill up pretty quickly. I shot around 10 GB while in Costa Rica for three weeks, and probably could've easily shot 2 or 3 times that much if I had wanted to.

The other problem is that if you have 10 CF cards with you, its a lot easier to lose one than to lose a portable drive. Especially while you're hiking somewhere trying to fiddle around with memory cards - I know I'd lose one. I mounted the HD80 on my backpacks' waist belt, had two CF cards, and switched between them as I needed to (one in camera, one in HD80 dumping files). Worked out really well for me.