When CF cards were small capacity and very expensive, I went for a CF card to disk storage unit. As my CF cards got bigger I was limited by the small (100GB) internal hard disk (couldn't be upgraded), so it didn't last long. Eventually the internal battery died and I couldn't get a replacement.

I'm alway worried about taking my Netbook with me because it may be damaged, so I now buy larger CF cards before each trip.

Lots of cards, lots of storage... but no backup.