"500 million users think so"...Wow. What a phenomenally pedestrian statement. "Gee, the masses like it, therefore it must be valid and useful!". Can you even stop to think for a second about other activities that 500 million people like? Are all activities that at least 500 million people participate in valid and useful? I think not. The argument that you are using to justify Facebook as being meaningful (based on mass appeal) is null and void.