We're still in beta, so you'll need an invite in order to actually create a project. Hit me up via email (my HN username at gmail.com) and I can pass along an invite if you're interested.
Or do you mean something that keeps the source code private? I never really understood the point of private source code hosting; if it's on another company's servers, it's not really private anymore, and I'm sufficiently paranoid to distrust it.
Further, I'd like to get my friends using a more sophisticated system of coding than emailing (or sneakernetting) zip files when they "remember" to. Some of the projects they need help on are contracting projects for companies, so public-facing anyone-can-access code is neither allowed nor acceptable.
A hosted arrangement means that it will also get backed up, and be more available.