I generally do not have a backlog of owned games. Sometimes I might have two or three games that I've purchased but have not yet played. But that's as bad as that ever gets. I just do not buy games until I'm ready to play them, or almost ready, at least. Once you start doing that, you might as well light your money on fire.
I do have what I consider a backlog though. That's just a list (kept in my head mostly) of games that I want to purchase and play. However, I'm not big into going back and playing old games. So, once a game gets to about 5 years old or so, I eliminate it from my mental backlog. I'd say my current backlog is in the neighborhood of a dozen games.