I tried them and really like the feeling. They also stay on the foot really well. The proctection against cuts works well.
But, mine did not last long. After 10 sessions I had holes at the heels and toes. I used them on rocky stony beaches at our local lake. Maybe there is less wear if you use them on sand only.
Right now I'm experimenting with this:http://www.vibramfivefingers.com/products/Five-Fingers-Signa-Mens.htm?activity=watersport
Not bad, but a bit more material and less barefoot feeling and I need some time to see how good the proctection is and how long they last.
I think a combination of both would be the perfect solution.
A knitted sock with a very thin base to protect the webbing from wear.