MULE is using ridiculous amounts of CPU on my Linux box. I have a 2 GHz Core2Duo, and right now MULE is using 117% CPU (where 100% = 1 core). Funny thing is, I'm just sitting at the beginning screen waiting for players to join the game. Nothing else is happening.
During gameplay, particularly during auctions and player movement, it sometimes goes as high as 193%. This causes the graphics to stutter and I miss out on things.
I'm guessing my version of Swing (or whatever you used as a display library) lacks hardware acceleration. It says 60fps at the bottom, but there's no reason a game like this needs 60fps... maybe you could include an option to throttle the frame rate? I don't think most people could tell the different between 20 and 60 for M.U.L.E.