I do have a virtualization cluster running on proxmox ve with 3 vm hosts and 1 SAN (migrated off of citrix xenserver, which works great until it crashes and requires complete restores of all VMs) and I use backuppc for the entire cluster (vm hosts and actual virtual machines).  I am using both the openvz containers for services like bind, dhcp, mysql, and web servers and use KVM for higher level stuff like specific windows apps on xp pro vms) I do all logins for the whole linux cluster via LDAP specifically to make sure UID and GID are the same across every machine.  With the centralized authentication and accounting, I setup a backupagent user on each machine and give it sudo rights to rsync and limit logins to that user account by host (the backuppc servers, specifically).  

I have a single backuppc machine backing up each server which is my 'stable setup' and then I have a secondary " test cluster" of 2 backuppc machine with DRDB syncing up the raid1 array between the two hosts.  one machine is a primary and the other rsyncs the backuppc config over so they are identical but does not run backuppc.  This link is over a 10Mbit wan link from my colo to my office (same ISP, nice) and is so far a wildly successful experiment running drdb with ssh compression over a WAN link.  DRDB does a very good job and 'catching up' to the relatively slow WAN link.  I have found that backuppc uses bandwidth in a pulsing fashion with high and low moments witch lets drdb gain ground during the lulls in bandwidth usage. (measured with iftop on the LAN interface and the WAN interface, and watching the WAN stay saturated and the LAN pulse)

I have another backuppc machine that is backing up windows xp clients with deltacopy(essentially cwrsync).  maybe 25 or so hosts on this machine.  I backup the entire "documents and settings" folder.  I use microsofts ximage to pull whole base level system images so I can restore that and dump the settings and files back over the top.

anyway, I am successfully using backuppc for production and am doing off-site replication and have done remote restores across WAN links.  my setup is constantly evolving as we migrate away from our old equipment on to more modern hardware and software.

good luck.

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