I'm curious how it is decided how many comments to display before the "Show more comments" link.
Sometimes I see a dozen comments on a question and no "Show more comments" link, in other occasions no comments are visible at all, only the link.
On Stack Overflow, it seems to be the best 5 (by votes) or the first 5 (if there aren't any votes).
On Meta, the per-site configuration is set to show at most 15 comments, unless the number of answers exceeds 30, after which even more comments are hidden by default. Other values are used on other sites. According to a January 2011 comment by Shog9:
As an aside, upvoting comments does not change the sort order of comments, but when there are lots of answers, or lots of comments, then comments without any upvote (or comments with less upvotes) might be hidden, until one clicks that "show x more comments".