ODIN vs. Nandroid backups? I've been told that ODIN backups are preferred to Nandroid ones, but I've only ever used the latter. What are the features that differ between them, and how is one better than another?

Also, if it is true that ODIN is better, and I want to use it, can I without a Samsung device? It seems to me that I won't be able to use it if I have an HTC, which is a bummer if it's really that good! In that case, is there another utility that is available for sans-Samsung Android users?
IIRC, one difference is that ODIN can change the filesystem to a different "format". for example, there are ROM for the Galaxy S devices that would change the filesystem from RFS to ext4. if you did a nandroid of the device, before you flashed the ROM, then decided to go back to the "Stock ROM", your filesystem would still be ext4. This could cause issues if it is not a filesystem that the Stock ROM can deal with, or expect.

As for, "Is it better", it does make it easy for Samsung owners to go back to complete stock, but Nandroid is still a full backup of your device at that time and could, essentially, work just as well.