How to provide proper backups for multiple Linux based servers?

How often do you backup your servers?

The standard backup is done nightly, there are a few backups that are done more frequently.

How do you ensure that all of your Linux servers are properly backed up?

The backup send a report with a good subject on success or failure. I check that I have received the status messages at least a couple times a week.

What do you backup, apart from the obvious /home directories?

Depends on the server, but I almost always want /etc, /root, and /var/lib/dpkg. I then add any data directories.

How do you ensure that backups are incremental, but still easy to restore?

I use Dirvish,

Dirvish is a fast, disk based, rotating network backup system.

With dirvish you can maintain a set of complete images of your filesystems with unattended creation and expiration. A dirvish backup vault is like a time machine for your data.

Dirvish uses rsync and the --link-dest option to hard-link identical files for each backup together. The backup is fast, it doesn't waste space, and restoring is as simple as copying files.