I also agree that a server clone is nice for a quick way to backup/restore but it does not work for your OD and Postgres Databases very well and can lead to corruption. I personally do not use Time Machine that much as it has been a car crash with servers in the past...once bitten twice shy. I know there have been improvements with Lion but we have always used scripts for OD, MySQL (now Postgres in Lion) and Crashplan for data. I have had TM with Lion Server on but yet to do any test restores ;-)

So really saying that i use more than one way to backup the data/settings as i just cannot trust TM...yet.

I am also looking into the serverbackup command as a backup mechanism for settings to replace the very useful
http://sabackup.sourceforge.net/ python script that i have been using on my 10.6 servers.

An interesting article for further reading for you sysadmins
http://krypted.com/mac-os-x-server/using-serverbackup-to-backup-lion-servers/