This is one step that unless you are on the metered Australian connections, man I would not be wasting my time in migrating this data.
Check the box on this one and go on.
What about non-R2 SBS2003 installs? I put WSUS on a member server. Upon activating WSUS on SBS2011 (and removing old GPOs), will clients happily pick up their new WSUS?
Just change the group policy to point to the existing WSUS on the member server and it will pick up from there.