For those of you who like lightweight and flexible casual shoes, try Go Walk by Skechers. I believe they are the lightest shoe one can buy. For ex: They say a men's size 9 weighs 6.5 oz.
I bought a pair a few months ago. They are very flexible... the most flexible I've ever seen. They can be machine washed. Imo, the "cups" or whatever they are on the bottom are kind of annoying. I feel like I'm walking on soft marbles. I don't like that. But I like how the laces can't come untied -- they don't have any. I've noticed a difference in the material. The lighter colors are a cotton blend whereas the darker and vibrant colors are a mesh. Skechers are generally junk and not worth the money but I think this shoe is one of their better products. I haven't seen the same type of shoe from another maker.