Wow, heaps of posts! Great!
Ok, my toughts on some of the issues debated here...
History monks: Should have the exclusive right to take Time Stop 1/day (sp) as an Epic Feat.
Balancing monks: add their class-lvl as a bonus to all balance checks.
Rincewind: Of course he's a wizard! He can't cast the Octavio-spell spontaneously, but it's the only spell he's got 'prepared' and as long as he doesn't cast it stays in his mind, ready to be cast.
Borrowing: I've made it a skill, exclusive to witches of course. The DC to enter the targets mind is 10 + targets INT-score. Target gets a Will-save to negate, DC=borrowers borrowing check. DC to return from borrowing is the same as for initiating, but increase by 1 for each hour of continuous borrowing. Borrowing a swarm of bees or similar extreme targets would add anything from 10 to 30 to the DC (DM's discretion).
Headology: Another witch-exclusive skill. Every five ranks give a cumulative +2 synergy bonus to bluff, intimidate, diplomacy, sense motive and gather info. Yeah, I know this equals something like getting 2 ranks for 1 skillpoint, but the witches are supposed to be really good at all those things. I find my witch-class balances out in the end...
Granny fast-forwarding the entire kingdom of Lancre a hundred years is an example of epic spellcasting.
Vampires: Come in to types, none of which match the MM one. There's the true, super-powerful born vampire and the vampire 'spawn' (ordinary people who's been bitten by a born vampire -a PC option). As for the vampire family the Lancre witches encountered, I'd say they've mastered some prestige class that's made them sunlight- and garlick-tolerant, among other things.
PC races: Yes, of course you gotta have zombies. We actually had a zombie PC in the one weekend of playtesting we did. Slipped my mind... The books featuring the Nac mac Feegle wasn't out yet back when I did PC races, but they definitely need to be stated as a PC race!
Susan Sto-Helit: A unique outsider with loads of spell-like abilities; such as continuous True Seeing, Teleport without error (at will), etherealness (at will)...
For all of you who say it can't be done: May you live in interesting times...