At work we have decided to backup some of our Hyper-V servers to disk using the built in Windows 2008 tools and then back that up to tape for rotation. You will find instructions for this process in this article.
Install Windows Server Backup (WSB) feature
start /w ocsetup "WindowsServe Backup"
From command line:
reg add "HKLM\Software\Microsoft\Windows NT\CurrentVersion\WindowsServerBackup\ApplicationSupport\{66841CD4-6DED-4F4B-8F17-FD23F8DDC3DE}"