So, in beta5, water is supposed to look nifty. Well, I noticed it slows everything down a bit. Not a lot, but if you rest next to a big lake in the Trollshaws, you might notice the difference with resting in a wooded area. (this behaviour happened to me on Ubuntu 10.04 Lucid)Water now uses OpenGL shaders
Personally I don't like the idea of graphics becoming too pretty, if if it slows things down (I know I can switch to pure ascii mode, but that's the other extreme)