I started riding clipless about 2 months ago now. I was warned to try a few rounds around the block, stopping and starting, before going on a serious ride. I did once around the block was too pumped, filled up my bottles, grabbed my tools, and went straight out. I have a really crappy ~2k down to the bike path, right through downtown, though, and I definitely took a spill. I think it was around 3pm on a weekday, so the streets were quiet and only a few pedestrians got to watch it happen - I wish I did - it was one of those will-I-go-or-won't-I situations at a light that often results in cars running reds, but I wasn't going to let that happen, so I stopped, still not used to the pedals.
Fell right over onto my left side, onto the ankle that I'd broken pretty badly (surgery, plates, the whole deal) less than five months prior. It was terror as I realized I was falling and the direction I was falling in, but it turned out alright - not even a bruise, really. It shook me up, but I was good to do my 40k and get home, noticeably more tired than usual because of the extra effort on the way in and out of the city. One thing that I'm happy about is that the tech at the LBS set my left pedal to a very low tension, in light of my healing ankle. I've only increased it a little bit since.
I've had close calls since - a dog off its leash that I almost cut in half with my wheel, and the other time, again on my way down to the path, almost got doored - fortunately, I wasn't going fast, but I had to grab onto the door and roof with both hands and struggle to get a foot out. Scared the crap out of the girl opening the door.
Wouldn't go back, regardless. I use toe clips on my commuter bike, and I feel so much less in control.