I find it strange that there is so little lore regarding one of WoWs most important game items.
According to the Warcraft novels, Hearthstones are magical artifacts (can be crafted by mages in lore) that, when activated, can transport the user (one person only, confirmed in the Shattering) to a preset destination (in front of a hearth/fireplace). The stone itself is engraved with two words (written in the language of magic, presumably). The first word is the name of the owner of the hearth to which the stone is set to, and the second word is home (ie, a Hearthstone set to Razor Hill Inn would say "Grosk Home").
But in lore context, how is it even activated? In the game, all we see is our toons doing some magic spell, but no stone is seen.
Also, why don't the armies of Azeroth issue them out for military use for their soldiers? If a city is under attack and the guard patrol is miles away, they could hearth back and help save the town. If a caravan stranded and they have no food or water, they could hearth back to town and live. What if there was an uprising back at the capital, and the nation leader was out on the other side of the world? He could be back within ten seconds to sort things out.