I know he's sponsored by a major shoe company and thus part of the "machine" but adidas makes some damn light shoes and he doesn't wear them.
In fact for the Beijing Olympics he was concerned about saving his legs through the 10k so he had adidas specially design him spikes with more cushion.
This is a guy who grew up barefoot but then when was able to obtain shoes, he did.
From what I can tell he wasn't plagued with injuries throughout his carreer either like a certain book would lead you to believe.