Yes, you rack up miles on Zwift. They won't count towards strava challenges soon to keep some people from getting their undies in a wad, but they certainly should count towards riders totals. For the first time trainer miles actually are pretty close to real world miles. You can't just hop on a roller with no resistance and rack up 40 miles in an hour, you have to do the same work as outside to move your virtual mass through the virtual world.
Cool...It definitely has it's place, and seems a lot more fun than just slugging it out on a trainer.