How many pink (purple) cubes are there?

In Antichamber, I have found little purple cubes in some secret areas.

Each time, the little purple cube was alone, started moving as I got closer, and escaped. At least, for one of the two purple cubes I have so far, there was a big digit "2" on a wall nearby.

How many purple cubes are there in total?

According to the Pink Cube Guide on Steam, there are 13 known Pink cubes. Nobody currently knows if this is all of them.
(People have found two more in the game files, but it appears they are either bugged or unfinished and left in there by mistake, as there is no legitimate way to get to them).

Note that one of them (the one in Many Paths to Nowhere) can be missed - if you don't get it when you first do that area, you have to start over in order to get it.

According to the developer, you don't get anything for finding them all:

They're in secret places, and working out how to solve those puzzles is the reward right now. Not the cubes themselves. (Source)

I've found nine of these, I don't know what they do.

1. The one that goes along the walls of the four dimensional art gallery
2. Top exit in "Four Different Exits"
3. At the bottom of "Down The Rabbit Hole"
4. Under the elastic platform in "Stairway to Heaven"
5. The back green wall at bottom of elastic platform at the end of "A Wall Without Stairs"
6. At the top of "Managing Resources"
7. Above the pink room of "Deja Vu"
8. Backtrack to the entrance during "The Chase"
9. Backtrack through the entry window in "Window of Opportunity" to the pink room.

2-5 travel horizontally, 6-9 in a 2-shape, the one in the art gallery goes along the walls of the entire room.

They don't move based on your position. They move when you mouse over them.

I don't think it is just a single one. If you visit several locations without pushing the cube, it shows in every one. Had it been just one cube it wouldn't show in a later location without it being push through a previous location, would it?