As part of the SQL Server 2008 R2 launch it was announced that SQL Server 2008 R2 now supports Hyper-V Live Migration. However according to MSDN only the Standard, Enterprise and Datacenter editions support Live Migration.
I’m not sure why those are the only editions which support Live Migration, but hopefully they will get this extended to the Workgroup, web and Express editions as those editions probably get virtualized more than the Enterprise and Standard edition databases do.
Denny