@Dr Herbie: This may or may not work for you, but I use CrashPlan+ as it gives me unlimited (woohoo!) backup capacity, the only caveat is that it's only for one PC.
To break it down
1. All data is on one PC, all other PCs have access to that library using a GB Ethernet connection. When Windows 8 is out, we'll setup replicating disks on this.
2. CrashPlan+ is used to replicate #1. The cost is $3 per month for one PC, $6 per month for a household for unlimited data.
3. The most important data is also replicated to SkyDrive
4. Home Server backs up all of the machines, but it may be dying so I'm looking to switch options here for PC backup...