I would say, on average, 1-2 sessions per week. I've been running a weekly Mage: The Ascension campaign for a while now, and usually if I miss a week, someone will step in and fill the gap. There's also the occasional weekend where my friends and I will hold what we call a "gaming tent," a reference to the fact that when we were in high school, we'd have gaming sleepovers in an eight person tent that I purchased for that purpose. These marathon sessions are usually eight to twelve hours long, divvied up into two or three hour blocks of time during which each of us take turns running, and last well into the wee hours of the morning. However, these are becoming far less frequent now, and usually don't include the overnight any longer.
All told, I think gaming occupies 4-5 hours of my life per week, with exceptions.