I personally play 2-3 times per week, plus some prep-time on other days, and this covers 2-3 different games, so the average per game is once a week. From my experience I've found that a lot of games/groups play once a week, or twice-per-month, on a repeating schedule (like every Monday, or every-other-Friday), same as Ziechael said. It is harder to find/form a group that can play more than once-a-week, of course it is possible to do this if you can find a other players with matching schedule / availability. If you are Game Master'ing it is easier to have something to do multiple days per week, if your game requires or benefits from GM-prep-time such as making maps, planning scenarios, writing stories and descriptions or drawing pictures.