My Emily, who turns 2 next week, was running around the back yard naked a couple months ago... playing at the water table and getting squirted by her 3 year old brother... suddenly, she stopped, right in front of me, and started taking a wiz all over the pavement. I had to quickly move my feet out of the way. Funny stuff!
I'd actually rather see a toddler running through the sprinkler in the backyard naked than see one with a non-swim diaper. Those get pretty gross looking when they get wet.
And like most everyone else who's posted, I'm only ok with her being naked in the privacy of the backyard with nobody else around.