Also, you can do plenty of weird stuff to your mac! I've been waiting for someone to try customizing an opendarwin kernel (XNU) and running it on a standard OSX box. Check out the caches in your home directory to see some of the wild configurations that you can just xml away. Maybe AppleRAID would be fun to use. Many of the UNIX(BSD/Mach) parts of OSX are free, why not take advantage of them?