2016 Update: Did this today for the first time and worked better than I thought. Not great, but good for a warm up. I made the squares 10 x 10 and mandated that the passers move to a new side. And in fact the servers got the better workout. But a good warm-up.
A simple drill designed to practice receiving and passing with some conditioning built in. I might make the grid a touch bigger (or at least progress to a bigger grid) and I might emphasize the communicative potential of the drill, especially as the players on the outside change position.