I've thought about doing it before, but I've never taken the time. Essentially those who participate will take a screen capture of their desktop background and post it on their profile.
It's a chance to show off your desktop and whatever other programs you run in the background (Rainmeter, Fences, etc). The goal is to give your desktop some internet time and have fun with it.
Post a link to your profile below if you want to do this and I'll definitely check it out. You'll be seeing mine soon! Cheers!