A handful a year. I don't understand how anyone can buy a game every two weeks, expect to finish them all, and still maintain a normal social and professional life. Like I'm in college. I game a lot, but only when I'm not in class or doing homework or going to parties or hanging out with friends. I love video games, but with so many games costing 10-20 hours of dedication, I can't see how anyone can seriously invest that kind of time in gaming every two weeks, not to mention factoring in replay value and online multiplayer. Too much.
I can say, however, that although party games are the games I own the least of, I spend half of my "gaming" time playing the Mario Kart Wii's, Super Smash Bros. Brawl, lotl the Mario Sports games (especially Strikers for the Gamecube), Sonic & All Stars Racing Transformed, Injustice: God's Among Us (I know it's not a party game), and COD Blops II- local co-op. It's a way that I can mix my love of gaming with my social life. I have friends that are the girliest of girls who never owned a game console, for example, who will join in on an Injustice "tournament" and love it, because it becomes a social experience through video games rather than alienating media divided by "hardcore" and "casual" like it is now.
It's more of a college thing though. By living in dorms, it's really easy to get a big group of friends to come over and play in the first place. And I mean every day, not just on weekends. If you're in college and have friends come over regularly, A Wii U (or even just a Wii) is a good system to have if you want to meld gaming into your social life some more. Crazy replay value. And yeah, I also can't afford to spend money on games every two weeks, lol. Not on a college income anyway, unless I spent all my money on gaming. I'm not counting indie games/VC games though. Those I buy all the time because they're so cheap. Like once or twice a week.
Edit: Another thing for my to not is that I often times buy games in bulk when they go on sale. Like there was recently a sale on amazon for Wii U games. I bought like 5.