I want to talk about mapping during play. I'm taking a tangent from a forum post, but this also indirectly ties into some posts on Delta's blog on the Fireball spell as viewed through the lens of Chainmail, The post was actually about playing with a revealed map, eliminating the need for the GM to call out room dimensions and also providing a play area for miniatures; I don't use miniatures, so that part is irrelevant, but I've been considering the issue of calling out room dimensions.
Back in the day, I and my friends played maps the way they were "supposed to be played", calling out dimensions. Except we didn't really play it right, because whoever was GMing would correct the map for the mapper, at least on tricky areas. We kind of defeated the whole purpose of requiring mapping, which is to provide an opportunity for the players to get lost.
What I'm thinking now is that showing players the shape of an area is just fine, perhaps should even be mandatory, but that calling out dimensions is counter-productive, spending a lot of time on fiddly details (which, as you may remember, is my bane.) It's basically a test of the player's ability to listen to dimensions and count squares correctly, which doesn't really seem to fit with what the characters are supposed to be doing.
I think a quick description of directions and shapes is sufficient in many cases. "You see the corridor continues ahead almost to the limit of your vision, then branches in a Y." "You look through the door into a square room with two doors in the opposite wall." Give more detail for whatever the players ask about. Use compass directions if the characters have a compass or dwarf. Draw a sketch for unusual shapes or complicated intersections. But if they ask for measurements, ask "are you pacing it out?" Otherwise, give the dimensions in relative terms: "the room is twice as wide as it is across." For distances, the scale of comparison can be the party's light source, since they should know the approximate radius. 30 feet for candles and basic lanterns (which use candles,) 40 feet for torches (because they're "bigger candles",) 80 feet for the bullseye (oil) lantern. Say, "At the limit of your vision" or give a fraction (halfway to the limit, a third of the way, probably nothing smaller than a fourth.)
What this does is it forces the players to make a sketch map instead of fussing about details... but it also allows you to partially reclaim something like the targeting mechanic described in Delta's blog for fireballs. Players should only know approximate distances relative to their range of vision, especially during an encounter when there's no time to map. Spell casters have to call off an exact distance, which might come out long or short; area effect spells thus have a benefit beyond merely affecting more than one opponent. For the infamous "Fireball that conforms to the dungeon's dimensions" effect, I wouldn't do any advanced math; instead, if a Fireball explosion is so close to an obstacle that it cuts off a fourth of its radius, I'd add that much to the opposite side, or to whichever direction isn't blocked; again, I wouldn't mess with anything more precise than one half, one third, or one fourth.