That trebuchet is easily the best I've ever seen - makes me ashamed of the one I put together not so long ago.
I saw the pictures on Brickshelf a week or so ago and was wondering - does it work? The one I put together flung a 2x2 round with an eye piece on top a fair way but I couldn't attain the high trajectory I was looking for.
Inspired by this I might have another go (only in black due to lack of brown lego for the minute!)
Keep up the excellent work
P.S. the other siege engine is just as stunning, they would have my army of crusaders running away