For Mac, I find this to be AWESOME (seriously): Go into System Preferences > Keyboard > Modifier Keys, then change Caps Lock to Control, which is helpful because Control is hard to hit, then install KeyRemap4MackBook, then enable the Diamond Cursor, which makes it so:

• Control+J is your left arrow
• Control+L is your right arrow
• Control+I is your up arrow
• Control+K is your down arrow

Basically, you hold caps lock, and then your right hand's default position on the home row is now sitting on your arrow keys. This way, you can use arrow keys without leaving the home row, which greatly increases speed. I'm now to a point where I cannot use another Mac without this installed.