My first installment is on Henchmen Experience (PHB 39, DMG 85).
According to the PHB, "you should expect that your character’s henchmen will get about 50% of the experience points which their share in the slaying of opponents and garnered treasure actually totals" (39).
The DMG gives an example of this, indicating that the total XP is divided equally amongst all participants, PCs and henchmen, and then the henchmen have their XP halved (85).
The way I consistently misunderstood this when running AD&D in the past was that I read that 50% as "a half share" which is not quite the same thing as what is written. In essence I treated each henchman as "one person" and each PC as "two people" for purposes of calculating XP shares. In fact, the rules as written say that a full share of XP is counted out for each henchman, and that full XP share is subsequently cut in half.
To see the difference, let's say a party of one PC and two henchmen earn a total of 1200 xp for killing monsters.
In my old not-by-the-book way, I would divide those 1200 xp by 4 (2 shares for the PC and 1 share for each of the two henchmen), and come up with 300 xp per share. So the PC (with two shares) would get 600 xp, and the henchmen would each get 300 xp. So the henchmen each get half as much as the PC.
But if you do it by the book, you divide the 1200 xp total by 3. Then you cut the henchman shares in half. So the PC should actually get 400 xp, each henchman gets 200 xp, and the other 400 xp (200 for each henchman) are simply lost. That's right, they just disappear. Nobody benefits from them at all.
Of course I left treasure xp out, since that will vary according to whatever payment agreement the PC has made with his/her henchmen. But the principle still stands. In effect, the henchmen will receive ½ xp for each gp in their respective shares, meaning half of the henchmen's treasure xp will be lost as well.
From a purely game-mechanic perspective, I find my corrected reading of the rules to be intriguing. Using henchmen at all literally wastes xp. So players have a greater incentive to not rely on henchmen unless they really need to. This may not be a bad thing.