We immediately got it out and compared it visually against a plain old Wii Remote, and now we can determine with scientific* precision that it looks exactly like a regular Wiimote -- except for the "Wii MotionPlus Inside" label under the Wii logo. You can see the (complete lack of) difference for yourself in our gallery.
The one thing you can't see in the gallery: the difference in weight. We didn't have a kitchen scale handy, but informal testing (i.e. picking them both up) revealed no perceptible difference in weight. The fact that the added hardware doesn't change the controller in the slightest suggests that the MotionPlus was a placebo all along, increasing the sensitivity of controls by making you think they were more sensitive. Either that or the gyroscope is really small. We're not ruling anything out. FlingSmash and the Wii Remote Plus will be out November 7 in North America.
*actually not scientific at all -- we pretty much just looked at it.