Cross-Platform Network Backup Solution

I'm looking for a cross-platform network backup solution to replace Retrospect. If you post a suggestion that I end up using (even in part), you could be the recipient of free stuff. Read on for details.

Without going into to much detail, Retrospect can't seem to consistently maintain a backup file set that exceeds ~600 GB using it's Backup Server function. Faced with sporadic "chunk checksum" errors, the backup set has to be frequently repaired or replaced. This has only wasted my time, served to degrade the currency of each backup, and furthered my distrust of the whole system.

The following is a required list of criteria for a replacement solution:

- Backs up to a network location.
- Covers both Macs and PCs. Note that it doesn't have to be the same software on each platform. I'm looking for a comprehensive solution, not necessarily just one software package.
- Backs up a specific list of directories.
- Updates the backup set instead of overwriting (e.g. sync vs. overwrite).
- Runs invisible to the user.

List of optional, but preferential criteria:

- Searchable.
- Supports an exclude list
- Smart checkpointing (e.g. keeps as many previous states as room allows).
- Configurable from a central location

Possible solutions I've found:
- rsync on both the Mac and PC to a Mac hosting an rsync server.
- SuperDuper on the Macs, x on the PC.

So what do I do? rsync could work but it might be time consuming to setup and troublesome to maintain. SuperDuper might work for the Mac, but that doesn't help the PC's.

Please submit your suggestions as comments to this post. If I use any of the posted suggestions I'll buy the person who submitted the solution an iTMS or Amazon.com gift card. Please use a valid e-mail address when making your suggestions in order to be eligible. Links to viable solutions are permissible.