Just so you know, at some point soon we will get the first site upgrade in three years, and … (drum roll)… nested comments! There will be a few other improvements too, but largely things will look similar. It has been a couple of months of work, behind the scenes, to upgrade my sometimes quixotic CSS code.
But if the site goes down, or you are not able to add comments for a while in the next few days, it is probably maintenance.
Apologies for the inconvenience.