[glckr]

man is universally known in the industry, and supported (to some extent, at least) by project authors/maintainers; this project will be forgotten by almost everyone (and start decaying) as soon as this post is off the front page here.

[kick]

This is the second time it's been on the front page, and the last time was years ago. Doesn't seem to be decaying. Actually, it seems to be improving.

[skybrian]

They're often used, but I suspect most people who read them don't know how to write or even modify a man page. (What format is it?) Also, Stack Overflow probably gets more traffic.

Whether documentation gets read or not probably depends on its Google ranking more than anything.