Based on recommendations from an earlier thread on this same subject, I decided to purchase the nylon mesh shoes from Sprint Aquatics. A pair (Mens large, 11-13) weighs about 2 ounces total, and on a recent trip into Olympic National Park they were great for kicking around camp and for fording a couple of streams than had blown out their bridges. The soles are thin foam, and I did have a few sharp sticks poke through them, but they stay firmly on your feet and it felt almost like I was walking barefoot in them. They fit snug enough and provided enough protection that stream fording was secure and easy, and they dry almost instantly.
The shoes do seem to run small - I wear a 10.5-11 shoe, and the Spring Aquatic 11-13 size (their largest size) is a good fit. I think anyone with feet larger than a size 11 might find them uncomfortably tight. And, since the entire top is nylon mesh, your feet/socks will get dirty if your camp is in a dusty area.
I have a pair of Croc knock-off's too, but the Sprint Aquatics are way lighter and pack in less space than a single beach flip-flop, and so they've won a permanent place in my pack. By the way, the shipping charges are a bit high for such featherweight gear, so I ordered 3 pairs to try and glean some efficiency for the expense.
The website is www.sprintaquatics.com