Puppy Cave is a good place to find spellbooks

[magpie]

... without having to go through the boredom of stair-hopping the Infinite Dungeon.

I usually take any spell-casting capable characters in there, and come out with some decent low-level spells: Magic Missile, Burning Hands, Light/Darkness, and other spells of that sort. It's handy if you're playing as a Necromancer, too, the extra spells in the early game can make it much easier to get to the mid-game.

I mention this because it's not mentioned in any other source (like the Guidebook), as far as I can see.

[Silfir]

You don't have to go stair-hopping in the ID at all to begin with. Spellcasters have increased drop rates for spellbooks, so you'd expect to find some just by doing standard killmonstertakestuff. I don't think the Puppy Cave has any bonus to spellbook drop rates, it's simply a relatively tame early game dungeon, last two levels possibly excluded.

BUGWIL-massacre and ID-stairhopping are good ways to kickstart a spellcaster to level 13 and a good repertoire, but that doesn't mean going the slow way is all that bad.

Diving for the HMV with a squishy caster, now, that's madness. And of course, I am but a gadfly to be lured by the radiating light of madness.

[JellySlayer]

This isn't due to the Puppy Cave being special per se; it just has a bit to do with how drops work. Puppy Cave has two high monster intensity levels, 5 and 6, on which the PC will get many more kills than average. In addition, lesser vaults like PC:6 have atypical item drop rates. On average, completing the PC will give a fair number of items simply because you have to kill a lot of monsters to get through. Particular items (eg. spellbooks) are no more common in one dungeon than in any other, however.

I always like checking the Puppy Cave as a caster because I've always had very good luck finding shops there. I might speculate on reasons why there could actually be more shops there, but it's probably just positive bias on my part.