I've been tracking the rate in which GUI skins (WindowBlinds / msstyles) since 2001.  What I do is see how many new skins are created each month and then check on the rate of creation.
It is a good indicator of how popular skinning is.  Now, from a purely competitive point of view, msstyles compete with WindowBlinds skins. But Stardock, as a company, benefits from and overall interest in skinning.
At the start of 2004 there were about 2,550 WindowBlinds skins and 1100 msstyles.
Now, April 12 there are about 2785 WindowBlinds skins (not counting GUI Olympics entries) and 1212 msstyles.
This is looking at ThemeXP.org mainly as the site for msstyles. deviantART is a good site too for msstyles but they get even fewer msstyles than ThemeXP does.
So since the start of the year, nearly twice as many WB skins have been made.
Yea, I know, yippie for WindowBlinds. But does it mean that the GUI skinning "craze" has peaked and it's starting to move back towards being a more techie thing? Obviously not good news for those who use uxtheme patching programs but WindowBlinds has really become really popular partly because of how popular skinning, as a whole has become.
Thoughts?