Even today with block-based snapshotting filesystems getting more and more popular, they're just not the thing I'm looking for when 1) backing up different filesystems and 2) backing up to a remote host, thousands of miles away. My weapon of choice to tackle this one is still rsnapsot - fairly portable (needs only perl, rsync, probably ssh) and does incremental backups via hardlinks if possible, so it's quite space efficient.

Minor nitpick: rsnapshot has this cmd_preexec parameter and I thought I could use this to (re)mount the target partition rw - turns out this is not how it's supposed to work, but this task can easily handed over to a wrapper script, which you're probably using anyway when backing up lots of machines.