What can we learn from this federated social network? Wiki is most often compared to Github but Diaspora is in second place.
Watching A New Kid on the Block
Facebook is a market failure that will never be displaced except by regulation. One weak example is the 'give me my data' requirement which might be hard to define.
Diaspora is healthy and growing especially in Germany. It also exchanges data with several similar networks.
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Diaspora is the largest repo in an organization by the same name. It is a rails app of 10,000 lines in 200 app/*.rb files. Nine of the ten largest files are under 350 lines. github 
169 ./controllers/application_controller.rb 169 ./models/post.rb 179 ./models/user/querying.rb 194 ./models/profile.rb 201 ./models/status_message.rb 220 ./controllers/users_controller.rb 221 ./controllers/photos_controller.rb 236 ./controllers/people_controller.rb 348 ./models/person.rb 612 ./models/user.rb
The project is properly referred to as diaspora* which google will search but not tally in trends.
The project hosts a mediawiki site that includes FAQ for users, developers and pod maintainers. A diaspora* pod is analogous to a wiki farm. Of all the questions a few maintainer answers stand out. faq
If you plan on running your pod over HTTPS then yes you will need a valid commercial SSL certificate. By design, federation will not work with pods that have self-signed or invalid SSL certs installed. We do this to ensure that all users in the network are able to use diaspora* without suffering from constant security warnings related to 'invalid' certs.
Once you set up your pod, you should add some contacts to start receiving content from other pods. It's a good idea to add some active diaspora* people to your contacts, because they almost all run their own pod, so your pod will be known by them and you will be easily findable from there. After you added a few contacts it's a good idea to make a public post containing the #newhere tag, announcing your new pod, to get even more contacts.
No you cannot make a private pod. diaspora* is built around the idea of a distributed social network. We want to build one network, not enable special interest communities or companies to host their own social network. A large amount of the development effort goes into making that one network possible and the whole user experience is designed around it. This not only means that other existing solutions often have feature-sets way better suited to that use case, but also that if we did implement a switch to turn off communication with other pods, there would be many broken ends in the user interface, which would lead to a bad user experience.
While the project itself doesn't restrict what kind of terms pods run on, we realize not all podmins want to spend time writing them from scratch. Thus there is a basic ToS template included that will be used unless a custom one available. There are also two configuration settings to customize the terms.
settings.terms.jurisdiction - indicate here in which country or state any legal disputes are handled.
settings.terms.minimum_age - indicate here if you want to show a minimum required age for creating an account.