In addition to adding new features (many of which are available as previews for Reddit Gold subscribers), the degree to which Reddit must scale means that they

In addition to adding new features (many of which are available as previews for Reddit Gold subscribers), the degree to which Reddit must scale means that they can't simply spin up a dozen new servers and call it a day. Due to issues they've encountered on Amazon's infrastructure (http://blog.reddit.com/2011/03/why-reddit-was-down-for-6-of-last-24.html http://blog.reddit.com/2011/03/why-reddit-was-down-for-6-of-...) they do indeed require engineering hours to design and implement more robust and scalable approaches to providing their service.