But for other answers, to the kind of lazy questions that save me the momentary hassle of consulting the docs, it's also kept me from the serendipitous learning that should happen in that process. Since knowledge compounds and makes it easier to learn other things later, overall I'd say the "lazy questions" on SO definitely have a significant learning opportunity cost.
Will it be a net productivity gain over my lifetime, including learning opportunity cost? Probably, but only because of those insane bugs I'd never solve on my own.
Edit to clarify: I'm not the one asking the "lazy questions" without looking around. But these SO results often rank higher than official docs for my google queries.