Problem: I have multiple AppleTV’s running XBMC on them all reading from the same central server. The issue was that the thumbnails might be on one and not the other, also watching TV series its hard to keep track of which episode I am on since I watch from multiple locations.
Solution: Doing some reading you can actually make all of the XBMC instances store data to a central server running MySQL. Why would you want to do that? Well there are a few reasons, besides having everything in sync across the board it also gives you the ability to resume playback from where you left off in another room.
Since I already had a server on my LAN which is providing the media via Samba and already has MySQL running for a development environment it was a pretty simple setup. I followed the tutorial here, which pretty much calls for making a MySQL user for XBMC and then I took it a step further and have all of the actor/movie thumbnails being stored on a network share too. I have included my advancedsettings.xml file which you need to create and add to each XBMC instance.
I decided to rebuild my whole library, which takes a little but but all said and done its a pretty nice setup and being able to resume playback from room to room is nice too. If you have a dedicated machine, and multiple XBMC instances I would recommend this type of setup.