I don't know if I should introduce myself or not since I have been a long time lurker of the D2 SPF. Anyway, been playing as much diablo 3 as I can manage (yey for the Blizzard employee that thought exams month is a good date to release the game).
I have noticed a slightly curious thing about armor, hovering over the stat gives you a tooltip that is worded in the following way: "Reduces all incoming damage from monsters at your level by x %" where x is a number between 0-100(I am guessing heavy dimnishing return at some point which makes 100 impossible to reach).
If you check the detailed stats you can also see that you have resistances for all elemental damage sources as well as physical which seem to imply that armor really reduces all incoming damage. This had me wondering how the armor stat stacks with the resistance stats? (My guess would be multiplicative)
Since I am kind of playing all characters in parallell I am still working my way through normal and have not had the chance to try this out (since +resistance mods doesn't seem to be existing at my level).
If they are multiplicative though 50% armor and 50% to all resistance would effectively quadruple your life pool (Just running numbers here, no idea if that would even be feasable with a somewhat decent damage output).
Does anyone have some more information on this or any official statements on the formulas that are used in the game?