I use Frogs on my road bike and touring bike. As Pcad stated, they are great if you aren't riding competively (or serious about it).

The 'accidently unclipping' thing has happened to me, but only when the cleats are worn.

Plus, you have to be more conscience of keeping your feet straight and not letting them turn out too much, or you'll unclip. Happened to me once or twice, but only when climbing.
I suggest, when mounting the cleat, to make sure that the front of the cleat is turned enough out so that when you move your heel toward the crankarm, there is only a slight movement before the stop (on the rear of the cleat) brings up against the stop on the pedal. This will help avoid accidently unclipping for those who have 'lazy feet'.