I'm using the exact setup I described in the opening post - a centralised MySQL database to hold details of all the media, and metadata, and (as I'm using Frodo) the artwork is managed locally by each box.
I have my server (Windows Home Server) running XBMC, and it is keeping the library up to date - but the advantage with a MySQL database is that any of your clients could, potentially, keep the library managed.
The only thing that Frodo does differently is how it handles the artwork (thumbnails, posters, etc).
With Eden, the PC that adds an item to the library also downloads the artwork. Because of this, to ensure that all clients get the artwork, you had to 1) manually copy these files onto each machine, or 2) "move" the artwork onto a shared drive, such as a network drive.
Approach 1 is a manual process (or a number of scripts), and approach 2 is more automated, but gives you latency in retrieving and showing the artwork, as it involves the network.
With Frodo, the URL of the artwork is stored in the main database, and then each client keeps track of which it has downloaded. The client then checks both the centralised database, and its local database. If a bit of artwork is missing from the local copy, it will download it.
This has the advantages that with the artwork stored locally, it's quicker to locate and view (especially with an SSD) - which speeds up the user interface - but the disadvantage is that each client requires local storage space to store this - if you have a large library with lots of extra fanart, this could get into the gigabyte range (but Eden did this anyway unless you centralise the storage of artwork)