As others have mentioned, they're light and comfortable.  I used to wear shoes like these, and have a pair of Vibrum Five Fingers, so I think they have plenty of padding.  They also slip on and off well without having to untie them.

Sizing wise, I wear anywhere from a 12 to 13 depending on purpose, so I went with a 13 and they fit well.  I'd say they fit like a 12.25.

I don't think you can go wrong with these for a cheap, light, comfortable, stylish piece of footwear for outside of work.

Update: I've had these for a few months now, and they're still great.  Extremely comfortable and light.  The only downside is that they don't breathe well.  My feet sweat a lot so they developed quite an odor, to the point where I had to use a shoe deodorizer.