Not every janitor here uses this function that marks the pic with "didn't like it enough to approve".
Being what would probably be considered a fairly casual user of the site, the approval process seems fairly opaque to me. The FAQs give some basic details, but on the operational end it is sometimes hard to discern what is going on.
I have seen some instances of what are clearly sequential images of the same subject by the same artist, and some are approved while others are not, and images get deleted because they were unapproved for three days. Maybe the reviewer was going through material by tags instead of by copyright, character, or artist, but it seems like they never saw the ones that were unapproved.
There's a "control panel," if you like; a set of "approve" and "don't approve for X reason" links for each pending image. These exist in the Moderation Queue page, which is a simple list of all not-approved and flagged posts excepting those the user has blacklisted listed oldest-first, and another on the top of the page when viewing such a post. Clicking one of the non-approval buttons hides the post from the Moderation Queue page. When any of the users with the "approve posts" flag on their account clicks Approve, the image is...approved.
Basically, people who use the modqueue will pretty much always be counted as having reviewed the post in the counts at the top of the image as they click one of the links to get it off their list. Some of us don't want to wade through posts we know we'll dislike so we take a different approach (see my last three posts in that thread specifically) and even though we've seen and passed on the image, we don't show up in the count unless we go out of our way to open the page up and click the link.