Over the years I have run into several situations where for one reason or another a backup utility such as dump or tar couldn't read a particular backup. For that reason, I like to periodically do a backup using another backup format. So I might use backuppc for my main backup system, but once a month do a full backup using dump onto a completely separate media.
I have been sucessfully using 8GB dual layer DVDs for some of my backups/archiving and now that the price of Blu ray has come down I am about to experiment with that. I have been writing dump format files to the DVD's and then writing an SHA256 checksum for each dump file so it's very easy to verify the integrity of the dump.
I am also about to try daily emcrypted backups to http://rsync.net along with periodic archival to blu-ray disk for one of my backup needs.
I have noticed that two of the recently mentioned backup packages, duplicity and storebackup appear to support some kind of block level deduplication where you can backup a large file, database or possibly even a disk partition, incrementally over the network. I am interested in trying that for backup up of mysql databases.
Nataraj