The Windows Server Core Team has posted Microsoft Support highest reported issues pertaining to Hyper-V in Q3 of 2009.  I recommend reading through these before considering calling Microsoft Support and logging a call, which can save you some money (or prepaid incidents).

Anyways a lot of the issues are pretty obvious (such as update to the RTM version of Hyper-V).

Have yourself a look and save yourself some money.  Full article can be found here.