This is probably one of the most frequently asked questions since we have released Hyper-V and SQL Server 2008.
I guess you all know we do support running SQL Server 2008 in a virtual environment ask explained here.

Like always there is no good answer to whether you should or should not run SQL Server in a virtualized environment, the only correct answers is: "it depends".

The nice people of SQLCAT have written up a whitepaper with guidance and best practices around SQL Server on Hyper-V. 
Please make sure you read this whitepaper if you are thinking of running SQL Server on Hyper-V so you have a good understanding of the consequences of running in a virtualized environment.

*EDIT*
Make sure you read this post by PSS which contains new information about our support policy around virtualization.