My son runs. He's not a sports star or courier, but a fearless three year old sent by the universe to test my nerves.
What's particularly clever about his escape strategies is that he spends time being still first, to allow Mommy to become distracted. I'm not sure if this is learned behaviour on his part, or innate talent.
An example would be a recent trip to the produce market, where he was remarkably well behaved. He stayed with me while we shopped, and stood beside me in line - until my eyes dropped to my wallet, only to look up again to see a flash of pink hoodie: his older sister chasing him as he bolted out the door (she comes in very handy ;-)
Others have struggled with him aside from myself - soccer coach, skating teachers, swimming teachers, and various friends and relatives. Oh my goodness he was just here - now where the (bleep) did he go?
His potty training has gone extremely well, aside from the fact that when we're in public he doesn't feel it's necessary for me to accompany him to the bathroom, once he knows where it is (on the bright side, he now waits until he's IN the bathroom before pulling down his pants).
In case you're wondering, I have tried restraints. He may be the only 37 pound normally abled kid who still occasionally wears a wrist strap and gets buckled into a stroller. He is also in stark contrast to the way his sister was at his age - she clung to me like holiday season weight gain, and had to be constantly peeled off my leg. As a result I have no prior experience with this phenomena and no clue as to when he'll see the error of his ways.
Hopefully it will happen before he can outrun me...