Spellcasters make horrible prisoners. Yet, spellcasters are usually the last person in an enemy group left standing. *shrug*
I'm well known for surrendering foes. If the tide of battle has turned and there's an easily identifiable cleric or paladin of a do-gooder redemptive diety, that surviving spellcaster, assasin, or grunt will very often throw up his hands and grovel for mercy with the best of them. And then try like the dickens to break out of whatever holding facility they've stuck him in, to plague them another day.
My players have threatened a pox on the genius that invented Templates.

I get alot of mileage out of templated and changed monsters.
To go along with my Templating flair, I'm feared for my ability to jank a CR to the last edges of space and time. Often we complete a hard-won encounter and I hand out XP and the players say: "You're ****ing me, right?" I sometimes give out a +10% Frank's A Rat-Bastage bonus for horribly challenging encounter design.
By the same token, alot of my players have me put their characters together for them, since I "can break anything". They give me a concept, I give them a viable character build.
But, as horribly challenging as the encounters may be, as tough as any monster may be irreflective of its CR, I've never had a TPK and I haven't had to fudge to keep from going there. It's something I, personally, pride myself on as a strength as a DM. The party is always in danger, there's usually a lynch-pin that can fail and send them all crashing down, but I stress them to the max and they always know they CAN pull it out if they think smart. It's hard to do.
--fje