Well its my first post and i just finished installing SBS 2008 on Hyper-v server R2 Beta with no real problems what so ever i expected it to run incredibly slow but i was pleasently supprised with the speed of it, there were a couple of quirks when it comes to adding extra hard drives etc you need to take the disk offline so it is not availible to the host operating system using the List Disk command at the command prompt, for example
type DISKPART
type List Disk
type Select Disk (number)
type Offline Disk
this them makes the disk offline and it is availible to the guest os in the hyper v manager, appart from that i am otherwise quite impressed.