When I did see problems with turns 'taking too long' it was the players who were disengaged when it wasn't their turns - not even all of them, the old 'wake me when the fight starts' type players slipped off into their usual comas - were the ones that complained. That kind of player really needs to be dominant, the center of attention, to be engaged, at all, when someone else is having their moment, they shut down. The most destructive spiral is when you get a player like that, and he gets the idea of 'leading by example' (because he's accustomed to dominating play) and taking really /fast/ turns, which exacerbates his frustration.