Have a look at SuperDuper from Short Pocket http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html. I use SuperDuper to maintain a bootable clone of my system drive. If that drive fails i can continue working directly from the clone, and then reverse the process back onto the replacement drive when the time comes. You can schedule the backups, and write to a disk image which can be stored on your drobo. The smart update feature (incremental) only copies new or changed files from the last clone, so its really a quick process for such a solid backup.

Another one to look at is Carbon Copy Cloner http://www.bombich.com/software/ccc.html, although with no experience I cannot provide any insight except for the fact that it is free (SD goes for $28). At the time CCC did not support incremental updates for Leopard, but that has now changed, so well worth a look.

I only rely on Time Machine for those accidental deletions and corrupted files, and a catch-net for a system restore.

Good luck with the new drive.