Its a relative metric, just like PR (page rank) mentioned earlier. They are often used as a rough guide to how a site is doing overall, and while people both over and under hype their importance there is still value in them. Its like getting a check up at the doctor, maybe he doesn't see some hidden cancer (DA inflation to scam link sales) but generally its good to for him to say hey your pretty healthy.
Not a bad rating just keep building good quality links (and others if you prefer) and adding value to the visitors to your site.