Flickr is for people that are professional photographers, or for serious hobbyists. I have thousands of photos on my computers, hundreds on Facebook (stupid albums of my drunk friends and my dogs and such), but Flickr gets my serious stuff - stuff taken from a tripod with my DSLR, stuff I edited in LR or PS, stuff I…

Facebook is hardly popular, it's just people feel forced to use it because everyone else is. People are waiting for something to come along and take its place, just a matter of time.