I love my crocs. That being said, I found them not to work very well on a long day in the park. I did get a "hot spot" on my instep from them, but not a full-blown blister. On the other hand, my feet weren't sore from the impact of walking so far since the spongy sole seemed to alleviate that. The biggest issue for me was that they make your feet sweat. I tried them with socks, but the socks kept rolling down.
All in all, I found a good pair of cross-trainer sneakers to be the best bet.