1. It really does take at least three coats to hold up any magnet other than the ones the
magnet paint people sell, and even then only their super strong magnets will hold up any paper.
2. If you do three coats of magnetic paint on only a portion of the wall, that part of the wall will be noticably thicker. (You can sort of see the line in the photo below. Or maybe I can see it because I know exactly where it is.
3. You can put it on with a foam roller, but then it will probably take even more coats because the roller puts on a thinner coat than the brush.
4. If you are going to use paint left by the previous owners of your house, you might want to check that it's not from before the dawn of time and full of latex boogers before applying it to the wall.
5. It's a relief when the project is done (other than a little bit of touch-up needed on the corners).