There was a great little Moroccan restaurant hidden in a small cubbyhole on Danzigerstr. for about the first half of 2007, but when I came back from the U.S. in late summer, it was already out of business. That guy did couscous dishes just perfectly; it's a shame. Restaurants in Berlin seem to be perpetually undercapitalized, so as far as I can tell, unless they happen to hit just the right niche and explode into popularity within 3 months, they're history.
Mr. 36C and I went to Barraka near Görlitzerbahnhof that I'd been meaning to try, but I can't really recommend it despite the extremely friendly service. The vegetarian couscous was adequate but the lamb tagine was dull, ingredient-poor and far too dry for a dish that should be stew-like. In my experience, only Kasbah is worthwhile, and it is rather on the pricey side. Good date restaurant, however -- nice location in Mitte, good attention to decor, nice low lamp lighting. And the food is completely up to my standards. It also has booze, as it's not halal (which in Berlin is virtually a death-blow against any restaurant).