Currently twice a week. With occasional extra games at weekends, or dropped in sessions to get over certain events that affect only my own PC.
Of course, at one point in University days I played 7 different campaigns a week (one each weekday night, a day off Saturday, and two campaigns Sunday afternoon and evening). Never again, for which I am grateful!
With the exception of the occasional Play-by-post, I only roleplay once a week, on average. Any more than that, and the daily duties start getting neglected for me.