Q:

Is a 'double move' one action or two, for the purpose of things triggering off ending movement?

When I 'double move' in pathfinder does that count as making 1 or 2 moves? Is there any reason to go against RAW for balance/sanity (see swarm example below)?
I understand that it would consume 2 'move actions', but I would like to know how it interacts when things trigger off ending movement. For example, does a swarm using two move actions in a round get to deal their automatic damage twice?
I have always treated them as 2 separate actions, but when I read the following in the rules I started questioning that:
http://www.d20pfsrd.com/gamemastering/combat

If you use two move actions in a round (sometimes called a "double
  move" action), you can move up to double your speed. If you spend the
  entire round running, you can move up to quadruple your speed (or
  triple if you are in heavy armor).

A:

RAW
It appears to be two actions, honestly much to my surprise.

Move Action
You can take a move action in place of a standard action.

So when you do that, you get two move actions. You can use both to move up to your speed, as separate actions.
Nowhere under full-round actions is any mention made of a double-move action. Running and charging, yes, but not the simple double-move.
Now, Swarm Attack reads as follows:

they deal automatic damage to any creature whose space they occupy at the end of their move (no attack roll needed).

I read “their move” here to be “their move action” rather than “their movement.” I do this because, grammatically, “move” is not really short for “movement,” while having an implicit noun for an adjective (i.e. action for adjective move) is quite common in English.
So yes, this would trigger Swarm Attack twice.
However, it’s always good to acknowledge ambiguities in the rules.
Should it be run this way?
I’m not sure. I’ve never seen it run that way, and I sort of doubt that most swarms were designed with that ability in mind, but I could be wrong; after all, I was wrong about this working in the first place. In any event, just because the authors intended it one way doesn’t mean that’s how I want to run it in my game.
For my games, I’d have to carefully consider the swarms I was or was not using, and what options my players had for dealing with them, in order to determine how I would rule this. In my experience, swarm damage tends to be low, but at the same time the majority of character classes have almost-zero ability to do anything to them.
So, for example, if my party consisted primarily of mundane classes, I really would not make swarms twice as dangerous as I thought they were, because I already considered them too dangerous by virtue of their effective invincibility. So, and I suppose it’s a houserule considering RAW, I would not allow swarms to double their swarm attack damage by double-moving.
On the other hand, if I was making a campaign centered around swarms, and expected my players to build specifically with swarms in mind, I probably would go ahead and rule this as RAW, and let swarms do that. This would allow the swarms to be more of a threat for situations where the players aren’t just enduring them, but are actively and effectively killing them. It would also open up a few more tactics for dealing with them, such as partial action denial, à la Nauseated.
If I anticipated swarms being an issue either way, I’d make a point of informing my players of this issue, since it’s unlikely that any of them have considered it on their own.
As for “verisimilitude,” or “seeing it through the game world’s lens” or whatever, that doesn’t really come into play here: swarms are explicitly an abstraction, particularly with respect to the Swarm Attack (using one lump sum rather than thousands of minuscule attacks), so it’s really impossible to say what makes more sense in-character; in-character, a completely different thing is happening.

A:

Although yes, you take two move actions to double move, I think the intent is that the swarm deals damage when its movement stops, not when its move action stops. 

Instead, they deal automatic damage to any creature whose space they occupy at the end of their move (no attack roll needed).

Is ambiguous, but it's what stands to reason when you view it from the game world's lens.  There is no "pause" between one move action and the other, it is continuous movement until the swarm stops. Remember that in Pathfinder the devs have explicitly stated their lack of interest in making legalistically correct readings when there is a clear intent. I have never played with a group that allowed swarms to do damage halfway through a double move; I would venture to say that it would go against common practice.
Similarly, the same movement can't incur multiple AoOs from the same creature in a round - this doesn't mean two move actions = two AoOs, this means the entire 6 seconds of movement.
In the end, yes "sanity" can always trump "RAW" - RAW is not a thing. You have some game books some guys in Seattle wrote to try to make fun adventures. They are not programming code or legal documents. Do what makes sense in the game world and it'll all work out.

