Lanefan said:
3. Wealth-by-level table, and wealth-by-town guidelines. Good in theory...but does anyone actually *use* them?
All the time.
In every 3.x game I've been in, the Wealth-by-level tables are standard issue for creating characters above 1st level so players can properly equip their characters (since in practice, most characters I've seen are created above 1st, either to join an existing party that's above 1st, or because the campaign is starting above 1st). Also, the NPC version a standard DM tool for assigning how much gear an NPC adversary would be carrying, and equipping major NPC's.
As for Wealth-by-town, I see it often used as a quick guideline of "can you get that here", a quick way of figuring out what is the most expensive equipment or services that can be arranged for in a town. If it's too low, it's not likely that you'll find anybody who is willing to sell (or make) a given item, or anybody who can perform the given service (like spellcasting).
My own say on things that are good in theory but not in practice:
Attacks of Opportunity. I like the concept, and something like it should exist, and I do generally understand them myself, but they do create an awful lot of confusion among the player base, probably more hassle than they are worth.
Grappling. Nearly useless for PC's past early levels, as everything becomes bigger and stronger, and grappling always seems to be something that immediately brings the game to a halt as everybody pauses to look up the grappling rules.
Turn Undead. It's better than the AD&D version to be sure, but it seems awkward, like it could be improved. Maybe something that forces undead to make a save with the DC being affected by how well the cleric rolls, and failing by enough makes them take damage, which could destroy them. It's more dice rolling most likely, but it seems like it would be more consistent.
Weapon Sizes. One of the few 3.5 changes I hated. You can buy a Large-Size Dagger and a Tiny sized greatsword, and sometimes the incompatibilities it creates are almost silly. Sorry Frodo, don't use Sting, it's a Medium-Sized shortsword, you'd take a -2 from using it.