Most of us already know how the Mursaat are using the bloodstones. But I started reading the Manuscripts booklet, and something occurred to me. It says the gods withdrew some of the magic they had given all of the races, and divided it into four parts: Preservation, Destruction, Aggression, and Denial, as well as a keystone needed to unite the other four.
With the eruption of Abaddon's Mouth, the stones were scattered to unknown regions, though I think I have a bead on where at least three of them are.
Assuming each stone represents one of the spellcaster classes and their brands of magic:
Preservation = Monks (as visible by the healing waters of Maguuma)
Denial = Mesmer (lets face it, no one else is as good at it)
Destruction = Elementalist (raw torrential forces of nature)
Aggression = Necromancer (forcing corpses to rise to fight again, even against their own former allies)
We know of one bloodstone, and I know which one it is. In the (go figure on this part, eh?) Bloodstone Fen, we have the first we encounter. This stone seems rather passive on the outside, becoming little more than a sacrificial ground. But the manuscript says that the powers of the stones started leaking into the surrounding area. What is unique about the entire northern Maguuma Jungle, particularly the waters? The natural healing aura (aka Mending Junior). So we have the Preservation stone located for sure.
The Preservation stone made Maguuma a lush jungle, filled with healing waters. Impressive in scope, no matter how you slice it. Assumedly, each of the other stones would be equally impressive, but in their own way.
Back to the manuscripts, it says that the various guilds found out about the stones being back in the world, and started the Guild Wars to claim them, fighting without ever gaining advantage for fifty years. Ending rather abruptly because of the Charr invasion of the human lands. Less than a year after the invasion starts, the Charr encounter an obstacle. The Great Northern Wall, standing tall and seemingly unbreachable. So, it is my belief they turned to their own, recently acquired power. Look at the searing. Even the Mursaat seem incapable of generating a single spell that powerful. At most they maintain something already made.
So with Preservation out of the running, and Denial and Aggression not fitting the bill, we have one stone left: Destruction. Seems to fit the bill very well. It obliterated most of a nation's cities and villages, burned the plant life to ashes, evaporated the bodies of water leaving only oily sludge pools in their place. If that isn't destruction, I need a new dictionary.
Moving on, we have Aggression, which I believe would be the necromancer's stone. What other events do we know? A year after the Searing, the charr were at the gates of Arah. In a blast that obliterated an entire nation, the southern charr army was destroyed. Less than a year later, after having just driven the charr from their borders, the people of Kryta are facing a new menace: An army of undead, wearing the garb of the Kingdom of Orr. As any good Minion Master knows, regularly created undead return to the less 'un' state in fairly short order. One of the Yaks Bend quests has you drive off Verata as he is working on his own spell (Verata's Sacrifice) in order to lengthen the lifespan of his pets. But we are looking at an entire army, able to spread across an entire nation, with no sign of the typical accelerated decay of normal undead. That sounds like something that a stone that embodied the powers of necromancy could do. And yes, the book says the Vizier used a forbidden scroll to cause the Cataclysm, so I may be grasping at straws here, but there is nothing that says the scroll isn't similar to what the charr used to cast their spell, needing someone who had sampled the power of one of the stones to unlock it.
So at this point, I think I have three of the four stones located: One in Maguuma, one in the Charr Lands, and one at the bottom of the crater formerly known as Orr.
This leaves one last stone to locate, but I have my theory on that too. I kinda think the Mursaat have it. Look at everything they use: Spectral Agony, massive degen and damage spike. Call this life denial. The Ether Seals. True to mesmer style, they deplete your power just being near them (though they use elementalist spells, which I find odd). This isnt conclusive at all, and it could simply be the Mursaat's own magics (such as animating the Jade Armors).
Thats what I have so far. Time for the jury to deliberate.