I still use some of the "Dragon" magazine critical hit tables, training rules, and the Comliness score from earlier editions of "Dungeons and Dragons." I try not to confuse combat or spell-related rules (fortunately, some of the guys in my current group are more up to date on those things than I am).
As for Comliness, I use it to measure attractiveness to other members of a species/subrace, while Charisma is for willpower, leadership ability, and personality across races. I also miss the relative simplicity of kits over prestige classes, and the AD&D2 "Compleat" series of books did a better job of summarizing races and classes better than most D&D3.5/D20 references, IMHO...