This really is a note to myself, regarding my FreeBSD setup. I use this section to jot down things that I expect to forget, because I use them rarely. Google is alright, but note-taking won't hurt anything. So here:
A couple of days ago PuTTY started to demand password authentication, which it shouldn't, because I normally log in with a public-private key pair. That was a good excuse to refresh my keys anyway, so I generated a new pair and overwrote the authorized_keys file. I hoped, again and without any basis in reason or logic, that the problem would go away as quietly as it turned up. It did not.
Fiddling with /etc/ssh/sshd_config didn't help either. What did help was fixing the home directory permissions: doing ls -l /usr/home as a super-user showed soon enough that they were drwxrwxr-x, when they should have been drwr-xr-x at a minimum. I can't remember when I changed them or why, but the problem is fixed with chmod 755 /usr/home/username. That this was indeed the fault of loose permissions was confirmed by a quick examination of /var/log/auth.log. The idea to look there came from here. Some further clarifications on ssh, including a sample config file, are available here.
The other thing I learned from /var/log/auth.log is that I am getting hit by a flood of unauthorized login attempts from the weirdest places every day. So far, so good.