While I don't doubt the legitimacy of some public sightings, I personally think an actual, in person ABDL sighting is quite rare. I have never seen anyone with that telltale bulge, a protruding waistband or least of all, someone bold enough to go out and about in baby gear.
I have however, overheard an interesting conversation once. I remember waiting at a bus stop one time, there was a couple there, maybe in their mid thirties, and the woman was fawning over her partner, pinching his cheeks, playing with his hair, I believe he said something to the effect of "Mommy, stop!" or something, who knows. Was he an AB? Chances are, no he wasn't, he didn't have any padding or bulges or childish clothes on, but then again, how many BFs refer to their GF as Mommy? Of course, they could have just been playfully teasing one another.
So, nope, I have never noticed anyone out and about that was wearing for pleasure rather than need. Heck, I don't think I've seen anyone out and about that was wearing for need either. Maybe a lot of ABs, DLs and Incontinent diaper wearers who do go out in public are making the effort to hide the fact that they are wearing, like Sophy above. If that's the case, it makes a legitimate sighting all the more elusive.