I continue to receive 'friend' requests on Facebook from people that I don't know. Sometimes we have 'Friends in common' which at least allows me to make a connection of sorts such as knowing they are an artist that works in a genre that I am interested in, and they have realized this based on our mutual friends. Or perhaps we obviously have a similar interest based on our blogs or other social media and I know of them at least. I am usually alright with that. But at least introduce yourself.
Still I don't understand why, if someone doesn't know me, they can't include a little note just saying Hi Wendy I am a friend of so and so He /She has mentioned you, or I follow one of your Blogs or something. If you can't bother to introduce yourself (which is rude anyway) and I see no connection and I don't know you, I am not going to add you. I don't make my FB public for this reason.