Was skimming over this post a while back and remembered it when i was working on updating my addon for patch 6.0.
Dont know if this has been said before or not but here we go.
GUID's are changing for the next expansion.
The new format for players are: Player:[server ID]:[player UID] (Example: "Player:976:0002FD64")
local strGUID = UnitGUID("player");
New GUID format:
http://wowpedia.org/Patch_6.0.1/API_changes#Changes
Old documentation on GUID:
http://wowpedia.org/GUID
Maybe you could use the server ID part of the guid to identify what server you are on (presuming that the ID are uniqe in the world and are persistant).
Combining that along with a hardcoded list of ID's in a library you could maybe get something working?