Hello, all. I'm new here, but I'm jumping right in. I just finished reading the annotations for WoA, and I've just read both Mistborn books in the past couple weeks, so I'm new to all the ideas and certainly whatever discussion has taken place here already. Forgive me if I'm treading old water. Especially since I'm gonna jump all over the place.
It's not a well-formed in my head yet, but learning about Ruin and Preservation from the annotations (obviously they'll be featured heavily in HoA) makes me think there's some linkage between the magic systems and each of these entities. I would say Hemalurgy definitely is aligned with Ruin--think about the process of gaining its power and who has had access to it in the series. It's very bloody and messy, requiring sacrifice to gain. In some ways, it reminds me of the Dakhor monks from Elantris.
You'll also note that the Steel Inquisitors, who from what I see have the greatest and clearest link to hemalurgy, enjoy torture and causing suffering, etc. Furthermore, everyone who has hemalurgy hears "the voice" of Ruin. For Marsh, it's strong enough to control him--probably so for all the inquisitors. For Zane, it appeared as "God" but he often resisted it. For Vin, it's muddled up with memories of Reen--and I think the interesting thing about Vin and something that will probably be central to the climax of HoA is how she's overcome the voice (and how Zane was desperate to--"You were supposed to save me!") through trusting. That prominent theme has something to do with it, I think.
So whatever it is hemalurgy explicitly does, it seems linked to Ruin.
Feruchemy, on the other hand, to me seems linked to Preservation. It's what the Keepers do--preserve knowledge. It's what the power is about--preserving speed, strength, etc. for later. With the exception of the Lord Ruler (and even with him, it was used to preserve society, albeit in a tyrannical fashion) it seems to be used for good ends. Although admittedly we haven't seen that many Feruchemists. But I think this is interesting, and I think it's also interesting how Sazed ended up with his jewelry embedded in his skin at the end of WoA--like the Lord Ruler had his, and Brandon made a point of bringing that up in the narration. I'm interested in how that plays out in HoA.
That leaves Allomancy in some weird nether territory, though. The mists draw away from people with hemalurgy--the mist spirit seems kind of schizophrenic, both deadly with Alendi's packman, and with Elend, and it seemed hateful toward Vin. Yet Vin also understood it to be saving Elend and trying to keep her away from the Well of Ascension--which was probably true with Alendi as well. There could be two mist spirits, a good one and a bad one, but Brandon seems to have indicated there's only one. either it's crazy or it's very utilitarian in its opposition of Ruin. Could the Deepness itself be part of Preservation, somehow? To me that doesn't intuitively click, but it makes sense that Ruin, in altering the Terris prophecies, would make the Deepness out to be the enemy and that would explain the actions of the mist spirit.
I think more needs to be said about the Terris religion, which probably spells out about Ruin and Preservation better. And we know that Allomancy can be gained from Snapping due to a traumatic situation. I think the "pain" of that trauma is a good thing that tends toward Preservation's side as well--you gain the power of Allomancy in order to preserve your own life. Certain kinds of suffering like that seem to offset Ruin's ability, like how Zane's cutting himself weakens "God's" voice.
Like I said, I'm playing with a lot of different things, so I apologize. But I don't think we can understand Hemalurgy independently of the other magic systems because they seem complexly interwoven, especially in the characters hinted at having it that we've seen. Vin and the Lord Ruler seem as if they possess all three, and it's hard to say exactly where the Inquisitors get their power from, though there have been hints that they require the sacrifice of a Misting (hinted at in MB1) or Feruchemist (the prologue of HoA).
There's more missing from the puzzle in the Lord Ruler, too--did he create the Inquisitors, or did they already exist? What's his interaction with hemalurgy? I think this goes back to the Terris religion, because he's the only character we know who had knowledge of it--and something in that knowledge probably gave him an understanding of how to access hemalurgical powers for his ends. And if he wrestled with Ruin at the Well of Ascension and took the power for himself, did he think that he could use hemalurgy safely with Ruin so weakened and controlled?
I also think, though this is probably obvious, the three magic systems are linked through the chapter symbols (once again like in Elantris). In fact I think the Ars Arcanum chart shows that the metals are represented by the symbols. The striking thing about many of the symbols is that they look like they have spikes in them in different places, like inquisitors do.
Sorry, this is quite a ramble for a first post.
Hope I've added to the discussion somehow.