I'm Eric, 36, and very new to running. In fact, I've only ever run on a treadmill. More of a fast walk, really.
I have some friends that are crazy about Vibram FiveFingers. I figured there must be something to this barefoot running thing, so before I take the plunge and buy some Vibrams, I decided for the past month to workout in the gym using another flat flexible soled shoe called Renaissance Moccasins. http://www.renaissancemoccasins.com/
As I bought them about 10 years ago at a Renaissance Festival, this made sense. They're very light and comfy, and the sole is about 6mm thick. I do occasionally get odd looks at the gym.
Perhaps some day I'll trade up to the Vibrams. Still not in the mindset to make such a purchase. The more I spend on the treadmill though, the more I think about it.