I have loved it for years, but every once and a while I want to get rid of the swirls. They are fun and very subtle, but now I have a new look in mind. I'm thinking I'm going to paint the insides of those boxes with a color slightly darker than the walls. Stay tuned for that one!
In our chocolate powder room, I used real wood for the chair rail (I wanted it real thick and chunky) and the foam stuff for the boxes:
The million dollar question -- how big do you make your boxes? It's a bit of math (ewwww!!) and some trial and error. First, you'll need to measure the wall. Then, decide how many inches you want between all of your boxes. I do a standard three inches all the way around:
I highly suggest starting at each end of the wall, and working in. So if any are slightly off, it will be the middle box on the wall. If it's off just a bit, it will look like it's supposed to be, since it's in the center. This has saved me a couple of times. ;)

Oooo, I almost for got our master bathroom!:

So I hope that helps! Did I make sense? Remember, you do not need a nail gun to do this in your home. It just makes it a heckuva lot more fun. ;) If you do it with a hammer and nails, you'll want long finishing nails and a drill bit to match. Drill into your wood first, then put the nail in and hang the molding. If you pound a nail in without a hole first, it will most likely split the wood.