I was thinking about the basic issues of having multiple untrusted servers and dealing with the issue of one server granting you a ton of XP for no good reason, or servers gifting you gold. I wrote this on slashdot but copy/pasting here.
XP and gold can be treated as a universal currency. All servers are assigned XP points based upon the users % spent on their server. So you have a central authentication system that knows user Z spend 40% of his time this month on server X and 60% of his time on server Y this month. Server X in total is slightly less popular and given its 1000 users and their time spent gets allotted say 4000XP, and Server Y with its more 1200 users who spend more time on it gets allotted say 8000XP.
Those servers can have their own internal economy and XP distribution systems, but when you leave the server the server has to decide how much XP and gold to give to this leaving user. It can give it 0, but nobody will use this server, it can give that one user all 8000XP of its monthly allotment but then would piss off the rest of the userbase
. Upon entering other servers that new server can have a conversion factor in the universal XP that user came in with to their local XP. Now I guess the real issue would be how to stop cheating servers that suck away a users entire XP and never give any back. I guess a universal rule that new servers can't take away XP, and trusted servers can't take away more than 10% of a users XP. Maybe special authentication system for when I user wants to voluntarily give away more than a certain amount to the server they are entering into.
So basically you have local economies mixed into a world economy, with a central bank granting countries the right to print their own money but defining the conversion factors would be set by the countries but require backing in a central conversion mechanism.