I just got back from a four day quickie (vacation, that is

) and I walked 8.75 miles (travel day-arrived at 1pm), 10.25 miles, 13.5 miles, and 5.25 miles (travel day-left park at 2pm). I mostly wore Teva's (the ones with the ankle strap) or the Mush ones. Mush Tevas are flip-flops, but are very comfortable and have a lot of padding. I can't imagine wearing the Old Navy ones for more than a few hours.
As for Crocs, I LOVE them and wear them to work (I'm in the medical field), but they can get a bit warm and I was afraid my feet would sweat.
**Along that same topic, I rode Soarin' next to a guy who took his Crocs off for the ride. Although the manufacturers claim Crocs won't hold in odors, they don't mention that if you have stinky feet and suddenly take off the Crocs, rather than absorb the stench, the funk is released for a 10 foot radius. Gag!**