Got one of these yesterday:
http://www.youtube.com/watch?v=q0o8CaQuYHg
It's a machine to measure swingweight.
To anyone who doesn't know, swingweight is a measure of how hard it is to swing a racquet (measured in kg·cm²) - higher numbers give more power, lower numbers give more maneuverability. It is probably the single most important specification of any racquet, and the bad news is that it can vary greatly from racquet to racquet - even though two racquets are identical models and grip sizes. It's a shame, but it's the price we pay for using cheap labor to have lower prices.
When I got the machine, I immediately started taking racquets off the shelf and checking them. It was very rare to find two models with the same reading, and many of them were off by as much as 20kg·cm² - the difference between the 12.6oz ProStaff Tour and the 11.1oz Pure Drive - a huge difference really. If you've ever had two (supposedly) identical racquets, but for some reason one of them is you "favorite", there's a good chance it's because they had different swingweights.
Everyone should encourage their local shop to get some kind of machine to measure swingweight. Previously, they were very costly, but are now much more affordable, so there's no excuse to not have one. Without this type of machine, there is no other way to accurately measure, and adjust, the swingweight of a racquet.
PS - This isn't meant as an endorsement of any specific machine - just a PSA to make people more informed.