Interesting--I love Sijiminfu for a quick, inexpensive place to eat near Wangfujing if I'm staying there, but I've never had the duck. My favorite there is the sauteed green beans (ganbian siji dou, right?). I've had the dish several places, and it's the best version I've had. $4 for a heaping plate seals the deal. (Of course, I'm not as well traveled as many within China, and I suspect there are places that take this dish to an even higher level).