I switched to the Merrell Barefoot Series. They are fantastic. Really work the calves and I think do more to prevent over striding. The better form and posture I now have running has made running long distances incredibly easier. Ran a 10K earlier this week and it barely fazed me. Prepping for a marathon just became a lot easier.
If you do go for them, I recommend breaking them in first by walking around in them and maybe some light running. I went for a four mile run as soon as I got them and got some serious blisters. You probably want to go a size down from your regular tennis shoe because you're supposed to get a tight fit. Here's a pic of the True Glove ones that I purchased: