Smashing magazine recently published an article titled "10 useful usability findings & guidelines." There's a lot of good information here for both core committers and themers.
Of the findings, I found myself disagreeing with only one - "Most users do not scroll." In my testing, I've found the opposite - so long as false bottoms are not present. To avoid false bottoms, make sure content or design elements run past the bottom of your browser. See illustration below.