I did a ride on the WOD rail-trail last weekend and it turned out to be one of those days when your hormones turn off the "retain several pounds of water" switch, so I had to stop several times more than usual. And I was so impressed with the porta potties along the trailside that I seriously considered sending an email to Don's Johns to thank them for getting a handle on the odor issue.

I do hate it when they're out in the blazing sun, though. Just too darn hot to be in there.

Also at super-crowded events like the Race for the Cure in DC, I won't even consider using them because I know they can't handle that many people.

BTW you haven't lived until you try using one that's on an incline while you're wearing inline skates.