It's easy to find out whether interest in customization is increasing or not, just look at site popularity.

But what about in skinning itself? The future popularity of skinning can probably be determined by looking at how many new things are being created.

But if you were going to create an honest and objective metric to try to determine health what apps would you pick?

I'd pick apps that fit these criteria:
a) Have existed for awhile.
Are likely to continue to exist for awhile
c) Are amongst the most popular in their class.

Here are the apps I'm thinking of using:
WindowBlinds
Msstyles
CursorXP
Winamp
WMP
IconPackager
DesktopX
Litestep
Hoverdesk
Talisman (version 2)

Now we could debate on whether say Aston shell should be used or ObjectBar or WinStyles or NeXTStart or Sysmetrix but I'm trying to come up with a list of really core apps that help gauge general interest.

With that in mind, are there any apps that you really REALLY feel should be included? I.e. ones that today already have massive significant popularity and are likely to continue to be there in the YEARS ahead (i.e. have staying power).