I know two kids of the same age, with very similar cognitive/academic profiles, but polar opposite temperaments. One is absurdly extroverted, while the other is shy to the extreme (curiously, they are very good friends). The extrovert was grade skipped twice (and subject accelerated) in elementary school, to good effect, while the shy one was subject accelerated, but not grade skipped, also to good effect. Eventually, they both ended up being homeschooled, which has also been positive for both.
I think personality plays into the effectiveness of a gradeskip, but, I would agree, at a level that is more complex and subtle than simply saying that extroverts do better.
