Regarding the crystal ball, note that using it is much like casting the Scrying spell...it is NOT an unlimited clairvoyance/clairaudience spell!
You do take one hour to 'cast' your senses out through the crystal ball to locate your subject (i.e. the spell casting time is 1 hour), after which you have 1 minute per YOUR caster level (not the caster level of the item) to watch and listen to the subject, assuming your Scrying skill check was successful to begin with. You MAY use the item multiple times per day, but each use does indeed require another hour to refocus on a subject -- even if you are checking on the same subject.
Also, as per the spell, the crystal ball does require that you have a creature as your target. If you have no real knowledge of the specific creature, then you must have something at hand which was once physically connected to the subject -- a picture, an article of clothing, a weapon the subject wielded, a lock of hair, etc. Such an item should preferable have been recently in contact with the subject -- and handled by as few other creatures as possible since -- because the DC will increase the more tenuous the link. That isn't listed under the spell -- it does give the specific bonuses for thhe type of connection however, see below for details -- but it makes sense to me that trying to scry the last owner/wielder of a sword would be a lot easier than trying to scry an earlier wielder, as each owner's psychic imprint is partially overwritten by subsequent owners...I will judge on a case-by-case basis in that event.
As far as what you can see and hear, it says you can see and hear the subject creature...but doesn't say what else you may be able to see and hear. My initial concept is that you can see and hear the subject -- along with whatever occupies the subject's space, i.e. if the subject is reading a scroll you can see what is on the scroll, if the subject is being grappled you can scry both the subject and the creature grappling it, etc.
So the crystal ball is somewhat limited in terms of for instance 'fully mapping out a complex in advance' -- but if you spend a lot of time observing a particular subject, you may be able to get some details about the area he or she lives in during the minutes you get to observe them and the 5' square they are in. A creature's 'face' determines the area you can see, basically, and depending on the creature's activities you may be able to determine a lot or just a little from any given scrying effort. Here is the spell description from the online SRD (System Reference Document):
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Scrying Divination Level: Brd 3, Clr 5, Drd 4, Sor/Wiz 4 Components: V, S, M/DF, F Casting Time: 1 hour Range: See text Effect: Magical sensor Duration: 1 minute/level Saving Throw: None Spell Resistance: No The character can see and hear a creature, who may be at any distance. The character must succeed at a Scry check to do so. The difficulty of the task depends on how well the character knows the subject and what sort of physical connection (if any) the character has to that creature. Furthermore, if the subject is on another plane, the character gets a -5 penalty on the Scry check. Knowledge DC --------- -- None* 20 Secondhand (the character has heard of the subject) 15 Firsthand (the character has met the subject) 10 Familiar (the character know the subject well) 5 *The character must have some sort of connection to a creature the character has no knowledge of. Connection Scry Check Bonus ---------- ---------------- Likeness or picture +5 Possession or garment +8 Body part, lock of hair, nail clippings, etc. +10 This spell creates a magical sensor located near the subject. Any creature with Intelligence 12 or higher can notice the sensor by making a Scry check (or an Intelligence check) against DC 20. The character may cast the following spells through a scrying spell: comprehend languages, read magic, tongues, and darkvision. The following spells have a 5% chance per caster level of operating correctly: detect magic, detect chaos, detect evil, detect good, detect law, and message. Wizard, Sorcerer, or Bard Focus: worth at least 1,000 gp. Cleric Focus: worth at least 100 gp.------------------------------------
Obviously there is no additional focus needed when using the Crystal Ball, as it IS the focus of the enchantment. You can indeed cast the listed spells through the crystal ball, which makes it possible (if you have the spells of course) to understand the creature being scried, read its stuff, and see it even if it is dark...and possibly, if lucky, detect stuff or even send the creature a message! (A useful way to manage your minions when they are out on a job for you, BTW...) If a spell doesn't work, you can try again, until you run out of spells or the duration lapses.
Note that once you have focused on a subject, you don't need to maintain concentration -- you have your caster level number of minutes to observe the subject but can interrupt that for spellcasting, bathroom breaks, whatever. Your initial focusing effort is enough to target the subject and have the effect last its full duration. You cannot switch subjects at will -- however, you MAY attempt to switch to another subject IF both the original subject and a new possible subject are both in view at the same time. Doing so requires a Scry skill check, failure loses the focus completely, success means the sensor switches from one creature to the other, and the new subject has the normal chance to notice he or she is being scried upon. However, switching subjects isn't easy -- the DC is 20 for the first switch, 25 for the second, and so on, with an additional +5 if this is occurring on another plane. (This whole switching subjects rule is a Drakaran house rule, I don't think it is normally possible with a regular crystal ball.)
Okay, I think that about covers use of a crystal ball -- did I miss anything? Any comments on the mechanics, pro or con?
-- Ernie III / DrakaraGM