First of all: Facebook like Google and many other US platforms - has opted in to "Safe Harbor" http://en.wikipedia.org/wiki/International_Safe_Harbor_Privacy_Principles
Which means they have choosen to abide to EU privacy regulations despite being based in the US by their own own choice.
The german law regarding pictures is however best explained by some examples:
1. You take a picture of a building. In front of the building are a few bystanders. You do not need consent of the bystanders to publish the pictures, because they are not the main subject of the picture.
2. You see a guy sleeping on a public bench and you think he looks kind of funny. So you take a picture where he is clearly identifiable and publish it by posting it on the internet.You have now breached his personality rights - not by taking the picture but by publishing it. Because he is the main subject of the picture and you did not ask for consent.
3. You see another guy sleeping on his own balcony. You climb a tree and take his picture. You have violated his personality rights just by taking his picture because he was in his own private surroundings.
4. You see a famous actress on some public event and take her picture. You can publish it because she is what is called in german law a "person of contemporary history" and you do not need her consent.
5. The famous actress is swimming in her pool at home. You charter a helicopter to get some pictures. This is illegal because she is in her own private surroundings and the exeptions for "persons of contemporary history" do not apply.
Personally I think those laws are quite reasonable. But you can easily see how sudden changes of social networks privacy policies can get you in trouble: Putting pictures on facebook only accessible for a small circle of invited friends or family is not illegal - it's like showing your family photo album. However if the pictures of your drunken friend at a party suddenly are public and visible for all you could be in a lot of trouble.
The question here of course as always is: Who is responsible. Only the user who uploaded the picture or other personal data? Or the social networking platform who display the pictures and make money.