From VMware:
In vSphere 4.1:
VMDirectPath and USB Device Passthrough with vMotion is supported
Migration with vMotion and DRS for virtual machines configured with USB device passthrough from an ESX/ESXi host is supported
Fault Tolerant (FT) protected virtual machines can now vMotion via DRS. However, Storage vMotion is unsupported at this time.Note: Ensure that the ESX hosts are at the same version and build.
In addition to the above, vSphere 4.1 has improved vMotion performance and allows:
4 concurrent VMotion operations per host on a 1GB network
8 concurrent VMotion operations per host on a 10GB network
8 concurrent VMotion operations per datastore
Finally VMware is allowing us to take advantage of the larger 10GBit pipes and allowing more than 1 vMotion at a time.