Obviously, the kind of people who use Octopress would already know this, but just in case.

In your WebFaction Control Panel:

• Click on Domains/websites
• Add your domain name (which has already been configured to point to your Webfaction server
• In Applications Create a new application
• App Category -> Static
• App type -> Static only (no .htaccess)
• Finally, in Websites
• New -> Choose your subdomain, App, and fill in the URL, which most probably would be /.

Enjoy the extremely fast load times provided by WebFaction’s nginx servers :).

Disclaimer: Webfaction link contains my affiliate ID