Nothing out rightly impressive about this world other than this is what my six year old son has been working on over the past two weeks. I started out with 0.3.1 with Windows clients on XP for both of my children (8 year old daughter plays with it as well) and we've since gone to 0.4.dev-20120106 on the server (Ubuntu). I found that the clients crashed on both of the XP installs, so we've since dual booted his machine to Ubuntu and he's learning to use Linux a bit now (overall this is a win in many aspects).
We're using creative mode for the ease of building and getting used to the world\play. I've put a couple of mods into play including Animals (figured how to "defang" the vampires by changing fighting.lua -> local damage_done modified to * 0 versus + 1 in the calculation) and things have been working out pretty well.
End result, we're enjoying this!

