I kept expecting a bright background image to load, or a dynamic popup to appear. Even fully loaded, the page looks incomplete.
I just did a quick article on the design:
Showoff.io feedback and design impressions -
http://nerdr.com/startup-showoff-io-first-impressions-and-fe...
Why the "Average user asks:" critique when the target audience (as you acknowledge below) is clearly technical. Anybody with networking experience, ie. setting up a web-server (even for local dev) will know what localhost is (they type it in their address bar to access the "local" server)...etc
I've been using OS X too long, since I instinctually thought the website was grey out / not active.
i'll chime in as somebody who likes it.
I even tried playing with the bookmarks on the top right corner to see if they would light up the site.