It's interesting to see that question show up, because we work so hard on the code. It makes sense that you'd ask it, though, because most of the changes are either not visible (like anti-spam or anti-voting-ring features), or are subtle. For example, you may have noticed more capitalized titles on the front page in the last couple days—but this is an experiment we're going to roll back.

One reason we don't do a lot of visible changes is that HN's minimalism is one of its biggest assets. Another is that users don't like things to change, and the internal pressures that cause companies to do arbitrary redesigns are thankfully not in play here.