In many parts of the world (probably not the US due to the broken cable monopoly system) home broadband speeds are increasing at a decent enough rate. I've now got 38 Mbit down and 8 Mbit up, which is fast enough to sync any new photos we take. We use JungleDisk and only pay ~ $14.00 per month for storing a lot of treasured family photos.
If I used a portable disk drive I'd have to make sure it's always offsite.