As to the original post, I've got an awful lot of house-rules written up (mainly tinkering with feats, classes, and spells), but after running a one-shot last weekend, with players I hadn't gamed with before, I realized (when ease of mastery of the rules was paramount, and extensive house rules were ruled out) just which house rules seemed indispensable (keen and Improved Critical, simple but important changes to dwarves, elves, and half-leves, 3.0e Power Attack), and which didn't. This was pretty illuminating, actually.