Did you mean the computer literate, esp. excluding 7-year old kids? (I started young though)
All the good stuff nowadays generally isn't free (and the free ones are just awkwardly placed- uxtheme for example). We have awesome technology like Dreamscene and WB5 (though it's been some time) but both have a rather steep pricetag for people who do not pay through the internet. (Everything looks cheaper in real cash.)
Besides that, there are a few communities that are rather snobby on customization noobs and all- are you gonna bother when you're pestered by that reputation alone?
Also, we have the issue of "good/bad" taste arguments. There MIGHT be a LOT of people customizing, but dare not show off their desktops just because they are afraid of being judged (bring it to a larger extent, like the reason some people really despise Last.FM)
And if I wanted a long term usable style I wouldn't want to invest much time. My current setup just has a WB skin and 2 floating bars- anything else is rather redundant and is probably gonna make my OpenGL applications suffer. And there comes the 3 stars. (j/k, obviously.
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A little OT:
Skinning IIRC used to be more about the community, with several people collaborating to make great things happen. Now I find that it's rather bare with the newbies and snobby-ists. And all about a contest of who's "more talented". What happened?
(Edit: D'oh, when did money come into the picture.)
