I think for most of us its common knowledge ... though flip-flops make our fee feel fancy free in the summer, wearing them can have some bad consequences. Last year during training I was especially careful with my feet, always wearing shoes with support and staying out of anything with a heel. As the Marathon approached I became even more cautious ... to the point where I would be wearing sneakers even if I was "dressing up" for something. As a runner, your feet are pretty valuable to you. And you can tell by how ugly they get during training that they truly suffer a lot of the brunt force of your workouts.
Not that this is the first study of this kind, but Womens Health has a recent article siting research that found
flip-flops to be the source of sore feet, ankles & legs. Turns out, when you wear them you take shorter, almost 'drag-like' steps. This throws off your ankle-to-stride length ratio.
After a long run my feet would always be sore and swolen, so I would throw on a pair of flip-flops to let my feet relax. Its not a biggie to throw them on ... we all do it! But, if you are going to be on your feet or walking for any period of time - think twice about protecting those wonderful feet of yours :)