I've had the same problem. The jackd package installed without errors, but the server hangs during the initialisation stage, and never returns the command line. If you add the -v verbose flag, you'll see (or at least I see) that the last message before it hangs is
Jack: JackEngine::NotifyAddClient: name = system
Maybe that would help some experts identify what the problem is.
It would be great to get this solved, as pretty much 100% of Linux sound creation programs rely on JACK.