Mike, they last me a long time. Of course, that's all relative, depending on how much a guy shoots. I've been using the same cube now -- the one I made in the how-to on that other thread --for a couple of years, and I've never had an arrow poke all the way through it. With a cube shape, I can turn it around and shoot all 6 sides, and the corners , too.
I'm shooting 740 grain 2419's out of a 65# recurve, and 545 grain 2018's out of a 45# longbow. Both arrow setups go in about 8 inches.
No broadheads with these targets though... broadheads tear the foam up bad and fast.