I have a network of Mac laptops and Mac Minis. I also have an old G4 running HornWare SharePoints that allows me to use my Drobo as a network share (AFS).
Time Machine does not appear to support backup to a network share and hacks to enable this appear to be fraught with unknown danger as message boards suggest Apple disabled this for a reason.
What is the best way to back-up up Macs over a network?
Time Machine doesn't notify you if it doesn't backup or have any sort of centralized overview mode on the server to see all of your backups at a glance. It is great for a personal machine, but for backing up a bunch of machines you are better off with Retrospect which will let you backup over network, email you on errors, etc.
A few cron-jobbed shell scripts using the built-in copy of rsync might be your best bet, though it's certainly more work than a turnkey option.