Right now the service is invite only, and it is simple to ask for an invite. Simply head over to joindiaspora.com and enter your email. They will add you to the invitation list and get an invite to you as soon as possible.
Before you scoff at a new social network, remember MySpace and how they made a lot of changes. Next thing you know Facebook comes in and crushes them. Obviously, I’m not saying that is going to happen again, but you never know with these sort of things.