As Facebook grows it is becoming responsible for the experience of more and more users. Even the smallest changes and tweaks to the site potentially affect millions of users. Still, the site has to evolve but doing so requires more careful planning and testing time than a startup may get away with. Some of the challenges inherent to a company this size were detailed in a Facebook note by intern Zizhuang Yang who has conducted several experiments relating to user experience over the course of the summer.

“Site speed has always been an important factor in the development of Facebook, even as the site evolves over time to become more feature-rich and complex. As we grow beyond the 250 million user mark, every small change to the site causes a huge ripple, affecting throngs of web surfers and their experience on Facebook,” Yang writes.

His work focused on three experiments, all relating to usability. In the first he wanted to know the impact of the site's loading speed on the user experience. The results were somewhat surprising as the slower page loads didn't turn the users away from the site; all users spent roughly the same amount of time on the site regardless of the loading speed. This meant that slower pages translated into less pageviews which, of course, means less ad revenue.

The second experiment was conducted to settle an internal dispute at Facebook. The engineers couldn't agree which was the best method for loading a page – either rendering elements as soon as they become available or waiting for the whole page to load before drawing it to the screen. It turns out that the first method was preferred in all cases despite having some inherent problems like the fact that some functionality may not be available until the whole page finished loading even though the button or link may have already been displayed.

Finally, Yang worked on a set of experiments meant to find the optimal amount of stories to be loaded and displayed in the News Feed. Initially Facebook introduced a solution that managed to satisfy both speed and content availability by loading 15 stories up front when the page was first loaded and a further 15 when the user would have scrolled down enough to need the additional stories.

But he wanted to see if this couldn't be extended to even more stories so he tested the feature with an additional 30, bringing the total number up to 45 stories in the News Feed. The results were so encouraging – a boost of over 20 percent in page views and time spent on the site for the casual users – that Facebook implemented the change for the entire site soon after.