I have a set of Head C260i and they come with the SLD 11 bindings as well. They're probably the best and most advanced bindings I've ever had. In the front, the piece moves 3 ways and the back moves 3 ways too. In fact, sometimes when I'm in a rush to snap in my boot, it moves to snap in for me, even though I'm not pressing down in line with the bindings.
Never snapped off by itself for no reason at all. It's snapped off when I've been in some problems like wipeouts. I'm not an "advanced" skier or anything like that... just an intermediate... but I'm told by guys at the ski shop that these bindings are supposed to be one of the best for my level.