Let me try to elaborate real fast. Will there be a thermometer so we can tell how hot or cold it is in any given location? Will body temperature be taken into account when things live under for a long time? Will things like insulatory and conductive materials be used at all to help protect from the cold?
Thermometer: no, not in dwarf mode (as far as we've heard, anyway). Adv. Mode already has this (shift+P).
Body temperature when things live under... ground? As of
11/07/09, there aren't major temperature variations in next version's caverns (except for magma-dwelling creatures, obviously).
It was mentioned a long while back that fixed-temperature creatures might become somewhat more vulnerable to hostile climates, but I don't know where that's at now: "Individual tissue layers on body parts can sluff off or boil now, after suffering melting/boiling effects while remaining intact for a short time. They can also be damaged by heat/cold/burning as before. I still have to handle temperature effects for liquid and gaseous layers -- the only vanilla DF cases are things like magma-men, which wouldn't currently take damage because they have fixed temperatures. I'll either put that off or move them away from fixed temperatures to just enough homeothermy that they can stand being in caves but not out by glaciers, or something. The more relevant applications might be mods involving water creatures that could freeze or boil during regular game conditions."
Insulation: here's the most recent word on it, sounds like it isn't changing that much from the current system:
how do tissue layers interact with environmental effects, like temperature and gases? Do outer layers insulate and protect inner ones? Can poisons and wounds affect that by, say, changing tissue permeability or exposing inner ones?
Temperatures are still tracked by BP, so insulation uses tissue properties but still just determines the overall number. There are some pervasive ramifications in extending it, so it's not necessarily an easy project. Wounds have some exposure effects, but not on temperature. I think contact poisons do a bit with it, but there are also some BP-pervasive effects where there shouldn't be.