Facebook celebrates its sixth birthday today. Just one year ago, Fortune put founder and CEO Mark Zuckerberg on the magazine’s cover in a story entitled “How Facebook is taking over our lives.” The site had 150 million users. Today, that number has more than doubled to 350 million users.

There’s no question Facebook has emerged as one of the most significant Internet companies of its time. At its current growth rate, it will surpass Yahoo (YHOO)  for unique monthly visitors within the year to become the third largest site on the net. Half of the company’s users log on in any given day. Average users spend 55 minutes a day on the site. More than 2.5 billion photos are uploaded each month.

The scope of Zuckerberg’s vision for the site is tremendous, and his success has yet to be fully determined. But on the occasion of its sixth birthday, let’s take a look at six ways it has shaped our culture.

1. New politics of friending: Facebook’s users have made the word “friend” into a verb. If you want to keep in touch with someone friend them, and if they’re bothering you? Here’s a second new verb that’s just as important: to unfriend. Also, friending is not restricted to people. The site’s users are actively friending plenty of pizza parlors and TV shows and magazines. (If you don’t believe me, friend Fortune Magazine. We’re kind and interesting and we’ll be there to listen to you.)

2. Love in a time of transparency: So much for hiding old photographs and sappy cards in a box in the basement. Now your photos—and wall posts and shared connections—live on in the cloud. Fiddling with privacy settings to cut down on heartache has become a rite of passage for any break-up. A recent New York Times piece entitled “Breaking Up in a Digital Fishbowl” sums up the challenges of this new communication medium for anyone leaving—or being left—by a lover.

3. Breaking news breaks faster: Whether the earth rumbles in Palo Alto or ripples in Port-au-Prince, status updates send the news of an earthquake speeding into our consciousness long before the fastest news organizations.

4. The new 911: Last September, two Australian girls, 10 and 12, trapped in a storm water drain used their mobile phones to signal for help—by updating their Facebook statuses. It raised concern among local emergency officials and sparked debate about how social media should be used in an emergency. But the girls were brought home safely. And in emergencies from demonstrations in Iran to the terrorist attacks in India, status updates and tweets have been instrumental in helping people find help fast and let loved ones know they are okay.

5. Privacy matters: Zuckerberg has always believed in giving users as much control over information as possible. Even so, Facebook becomes the stage for a major user uproar over privacy every year or so. After getting flack for confusing privacy settings, Facebook rolled out privacy settings that are flexible and powerful last December. Using a simple drop down menu to the right of each post or photo, Facebook users can define who sees it. These settings have drawn criticism as well as kudos, however, in part because they are complex.

6. Getting together for good: Within hours after an earthquake struck Haiti in January, people turned to Facebook to express their concern. In the 24 hours following the earthquake, 1,500 status updates containing the word “Haiti” were published every minute. Thousands of dollars were donated through the “Causes” application on Facebook, according to Facebook’s Randi Zucerkberg in a blog post, and nonprofits mobilized to beef up their Facebook pages. As the response to the Haitian crisis demonstrated, when a lot of people have an easy way to give a little money, the philanthropic dollars add up fast.