I received an error while trying to vMotion today:  "A general system error occurred: Migration failed while copying data. Busy."  The issue turned out to be a swap file change in 4.1.  To get the machines to vMotion again I had to change an advanced setting:  Migrate.VMotionResolveSwapType from 1 to 0.  Then everything migrated after that.

Hopefully this will save someone the hour I spent with vmware tech support figuring this out.

-Jason