Just had just had a look at that and a few other demo vids and I'm seriously impressed. Now THIS is what minecraft has been missing! There are so many practical applications for this that redstone and iron suddenly become so much more valuable. My favourite machine so far has to be the automatic bridge builder. It's just a shame you can use it in the nether (is uses water) because that'd make navigating those lava lakes so much safer. Actually, if you set up a similar device down near the bedrock you could (in theory) set it up so a slice of the world gets pushed up one block at a time and all you need to do is stand there with a switch and a pickaxe and just wait for the ore to come to you! Another one I found impressive is a light switch mechanism that slides a block of light stone over a glass block in the roof and back again. I think this simple mod will really inject some life into the games, which let's be honest, has been getting a little stale of late. So what's next I wonder? Flying mobs and dirigibles!?