Well, I've hear people say it would happen, read about it happening to Lance Armstrong in a race once, and was warned when I bought my pedals.
Today, I fell because I didn't get unclipped!
It was only my second ride outside with my Speedplay Light Action pedals, and I went all 18 miles without a hitch! But, I pulled into my lower driveway (we have a small garage under the house and a 2 car detached garage on the side, so we have 2 driveways) and looked up at the upper driveway wondering why my wife didn't pull her min-van into the garage. I unclipped my left foot, leaned to the right, and down I went!
Small scrape on the new Brooks saddle (proofride should fix that,) goofed up the tape on the right side of my trekking bars (color matched electric tape fixed that,) and scraped my knee a little (time will fix that.) Worse part was that my wife saw me go down and will inevitably rib me about it now and then (I love her.)
Oh well, lesson learned. I'm sure it will happen again, just hope it's not tomorrow