Facebook is a time suck. According to Nielsen data from April 2010, the average person spends six hours on Facebook per month.

There is a simple reason people spend so much on Facebook — engaging, borderline hypnotic features. Login to Facebook to add a friend and suddenly you’re sucked in by notifications of friends commenting or “Liking” your posts, photos of friends and family members and news flowing in from your favorite Pages.

Facebook — moreso than any other social network — has mastered the art of building features that demand attention and speak an emotional language that extends beyond a single country or demographic.

The News Feed, a controversial feature when initially released, is perhaps the most engaging of all, as it draws the user’s attention to the flow of content from his or her friends. It eliminates the “what now?” moment that online users face when logging into any site. Even with just a handful of friends and a few “Liked” Pages, the average Facebook user is presented with a myriad of things to do, most of which have a feel-good quality about them.

On the features front, Facebook has also managed to build the world’s largest social platform, extending users’ social graphs to their favorite games, applications and websites both inside and outside of Facebook. Whether you use an iPhone or iPad app to check the feed, or fire up a new round of Farmville, your Facebook friends are right there with you. It’s this relationship-oriented context that makes everything — even the most bleeding edge ideas — seem familiar, if not fun.