Being in the biz for quite a while, I've heard both sides of this argument. Disks are definitely faster than tape - that's a given. The cost points are also getting pretty tight.

Drives, though, haven't changed much in their ability to take abuse. Tapes are pretty resilient to a drop from waist high, where as a hard drive may never work again.

If you decide to use disk backups and ship them off-site, I only urge you to use proper packing for the drive(s) to mitigate any damage during shipment - foam, use hard shell cases, etc. I'm sure this goes without saying, but I want everyone to be sure that they understand this difference. Tapes still need packing, but are not as fragile as the disk platters, heads and movement mechanisms.