I have created yet another backup script, since the previous one although correct worked only under VMM 2008. And VMM 2008 in its current BETA (+hyper-v patch) is still a bit unstable and the script caused the host to hang for large VM backups.
The script I created is a script that saves, exports VMs (and then starts if VM was running prior to starting the script) to a target local folder. Additionally in the batch file you can add a robocopy command to copy that to a remote location if you need.
The script works currently only locally (though with psexec it should be able to modify it to run remotely as some commands are local folder/file operations) and requires powershell.
Another script I found on the internet is available here: http://mindre.net/file.axd?file=CreateVmBackups.ps1. Unfortunately this was AFTER I worked on mine;)
A ps1 and batch file to launch it are attached.