Phil,
Here we Sync SEPM with AD, that creates all the OU's in SEPM. We only really have two locations, 'in office' or 'out of office' based on client information, in the office uses a live update policy that uses a GUP.
Our GUP's are defined by a registry key which makes use of the new GUP list feature added in RU5. A client will choose a GUP based on it's network location.
This however has nothing to do with the update packages (install packages) as these are set on the OU level. If a client chooses to roam to another site then this will mean that the update may not be local, but in the majority of our cases this has worked fine. This is why the feature request for client version updates from local GUP's will be a great addition to SEPM.
We have also set a dedicated machine to be the 'optional GUP' if no other GUP exists for the site, in the live-update policy to catch clients such as 3g.
Best Regards,
Paul