I've seen a few "hard to clip out" comments in this thread and just wanted to reiterate the benefit of reading the instructions that came with your pedals and reducing the retention spring tension to the lightest setting that prevents accidental clip outs. I've seen riders new to clipless have to jerk their foot off of the pedal to unclip, that isn't a fault of the SPD system, its a sign of too much spring tension. Extremely powerful and aggressive riders may need more tension depending on the type of riding they are doing, but the majority of riders will find fairly light settings perfectly adequate. It's also helpful to occasionally clean out and lubricate the mechanism and check the tightness on the cleats (I'm a fan of SPD multi-release cleats).