This friends network is a second advantage of Facebook. While on the classic dating sites, you spend hours trying to get a clear picture of the personality of that particular sexy lady, on Facebook you rapidly has an idea of who she is, who she hangs out with, and what things she likes to do in life. So it is less scary to contact that lady and connect with her.
You also have an idea of what are her interests, social circle, education, and her best friends - because you know some of the people she is best friends with.
And you have a subject to start with, an opening phrase if you like, based on your common good friend. And you might get an idea of the places she goes out to party, which might lead up to a "accidental" meeting and connecting in real life.
Dating on Facebook became even easier with the "dating applications", like Zoosk. Zoosk has 20 million single FB-members, and a very, very active chat room. Their members, called the Zooskers, are looking to meet up for a date in their city.
That's a whole lot of things that the regular dating sites like Plenty of fish.com and Meetic don't offer yet.
Three more advantages of Facebook for dates:
Some things to look for when dating on Facebook
Review of datingsites and comparison with Facebook
How to use Facebook to find a date ?
Dating with Orkut and Facebook