The amount of latency between a user's input on a game controller and the in-game reflection of that input is an incredibly important factor when comparing motion controllers. Sony has been boasting that the input latency for the PlayStation Move would be "under a frame" -- though Digital Foundry concluded otherwise during its brief tech demo with the sphere-tipped peripheral.
Digital Foundry conducted a fairly rudimentary experiment in which a person filmed himself sharply moving the controller, then counted how many milliseconds it takes for the screen to reflect his movement. Though there were a few variables to the experiment (such as the unknown, natural latency of the television display used in the demo), Digital Foundry estimates the device's latency to be in the ballpark of 133ms (around eight frames), which they claim is "fine for most of the applications you would want from such a controller." You can check out a video of Digital Foundry's simple latency experiment on Eurogamer.