Re: OT: Nethack
Altars are extremely good for a few things:
(1) You can definitively and easily tell whether any item is blessed, cursed, or uncursed by dropping items on it. This can be done regardless of whether the altar is converted.
(2) If you sacrifice enough stuff, your god will reward you with a gift. The gift in question is usually (though not always) an artifact weapon. Many classes have a guaranteed first gift which is particularly geared for their class (though other classes can use it and can receive it as a gift). For barbarians, their first gift is Cleaver (a battle axe that does a substantial amount of extra damage and, incidentally, what my barb was wearing when he reached demigodhood). If you've got enough food and can handle what's nearby, it is often not a bad idea to sit around and sacrifice corpses until you get a gift, though if you start running out of food, stop and come back later. Be warned that receiving a gift from your god will reset your prayer timeout, so be sure you can pray again before trying to.
(3) It allows you to check whether or not you can safely pray. If you attempt to sacrifice something and you have "a hopeful feeling", you cannot safely pray (though you just got closer to being able to). If you have (IIRC) "a feeling of reconciliation", you were not previously able to safely pray but are now. If there is no message, or "a four leafed clover appears at your feet", you can safely pray. For the record, if you're in sufficient amounts of trouble, prayer will sometimes succeed even if you "can't safely pray", so it's still worthwhile to try if the only alternative is death.
(4) The reason I'm usually talking about trying to convert altars is that if you are standing on an altar and have potions of water dropped on the altar and you pray, you are doing what's known as a water prayer. If successful, it will convert all the potions of water into potions of holy water, which can then be used to bless items or uncurse items. You can turn potions of (something useless) into potions of water by dipping them in to fountains (and a few other ways, but this is the easiest). Be advised that anything bad that can happen from quaffing from fountains can also happen from dipping in fountains, but generally by the time you should be worrying about making holy water, you can take water demons, nymphs, and moccasins.
As a side note, while using a non-co-aligned unicorn expedites the process, you can convert an altar by sacrificing pretty much anything (though it sometimes takes a couple tries). Never, ever, ever sacrifice a corpse of a pet (personally, I refrain from sacrificing any cats and dogs just to be sure) unless you want an extremely displeased god. Never, ever, ever sacrifice a corpse of the same race as you (might only be limited to humans, I'm not sure, but I'd recommend not sacrificing either humans OR whatever race you are) unless you want to meet a major demon. There are, as always, exceptions, but they're rare and still not a good idea IMO.
Regarding scrolls and general identification: my personal method is to not use any scrolls until I know which one is identify and I have holy water. Blessed scrolls of identify have a 20% chance of identifying your entire inventory. After soko/mines end, you should have ID price-identified and should have a pretty large collection of unidentified crap. Bless all your scrolls of ID with that handy holy water I mentioned earlier, get everything you have that isn't identified in your inventory (dropping tools/armor/etc if necessary, but be careful something doesn't come up and pwn you), cross your fingers, and start reading blessed ID scrolls. You CAN price-id scrolls besides identify with varying degrees of certainty, and a variety of scrolls can be used by monsters which will cause you to identify them, and you can ultimately identify scrolls by reading them (which is potentially very bad), but I personally just wait until I can know for sure what they are. You may not necessarily want to wait, though, because this point (for me) doesn't generally come until the midgame, so you'll be without the benefit of basically any magic items for the entire early game.
Quick scroll price-id summary:
ID - base price of 20
Light - base price of 50 (not worth buying)
Enchant X - base price of 60
Enchant Y - base price of 80
Remove Curse - base price of 80
Everything else - base price of 100+ probably not worth your while for the moment.
I forget whether enchant armor is 60 and weapon is 80 or vice versa. The base price is modified by your charisma (check wiki/spoilers for exact modifiers), but the annoying thing is that there is a random 33% surcharge, and in case you didn't notice, at least a couple of things are spaced out such that base_price_A * 1.33 = base_price_B, so it is not always 100% certain.
If you want to be sneaky, though, when you're selling items (regardless of whether you accept the offer), your charisma is not factored in, so you will always receive either 50% of the unmodified base price, or 33% of the unmodified base price. The useful thing is that, unlike buying (where the particular item is going to be a fixed price no matter what you do), the shopkeeper makes a different offer each time you attempt to sell something, so you can repeatedly drop it, refuse the sale, pick it up, and try again to determine the exact base price. The drawback is that it has to be an item type the shopkeeper will buy. General stores are handy for this (and there is almost always one in minetown).
-CG
edit: With all this talk of altars, I just wanted to point something out. Do not attempt to convert the minetown altar. If it starts out coaligned, great, you can sacrifice at it and make holy water and whatever, but if not, just stick with using it to identify B/U/C. If you attempt to convert it, the priest will become rather annoyed and probably proceed to kill you very quickly. If you're high enough level you can take him, but it's a pretty high level.
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