I've heard Go has obtained some sort of mythical status as a test of intellect... I recall somebody claim that Japanese kids grow up smarter than North American kids because they play Go and it develops their brains to think in ways that playing with Nerf pistols just can't.
Yikes. I would expect that learning to play go develops certain skills wrt spatial visualization which could mean better results on certain types of tasks like IQ tests. I don't see it as something that generally increases intelligence. They say the same about learning an instrument or a 2nd or 3rd language - but the latter two are more useful social skills in addition to the intellectual boost.