I ran across a silly configuration issue today when creating a Wiki page library for our group's collaboration site. We don't use the Quick Launch left nav sidebar, instead favoring the Table of Contents web part. I created the Wiki library, but it didn't appear in the web part -- it should have shown up under the "Documents" section below.
What's up here? A quick check of the navigation settings (under library settings -> Title, description, and navigation)
...revealed the silly error I'd made. I mistakenly set the display on Quick Launch to "No" instead of "Yes." I flipped that switch:
... and things are now displaying as they should.
Just because you don't use the Quick Launch doesn't mean you shouldn't make items available via it...