Can't connect to PostgreSQL on VirtualBox guest
OK, I found the missed step thanks to this post.
I had forgotten to set the listen_addresses setting in postgresql.conf. I'm using this value, but it could be more restricted:
listen_addresses = '*'
Just to clarify, when you connect to PostgreSQL from the host, use localhost as the server and 5432 as the port. VirtualBox will forward that port to the guest.
I also realized that some settings require you to restart PostgreSQL instead of just reloading it. The command is:
sudo /etc/init.d/postgresql-8.4 restart