I don't own any machines. Here in Seattle we are lucky to have dozens of well maintained machines on location. I just don't have the money as a college student to buy any games. If I could, I would buy a couple of the really fun early Bally SS games like Flash Gordon, Skateball, and Frontier. Otherwise, I can pretty much play any WPC or Stern I want somewhere in town. As a tournament player, I more or less have played every good game out there to death so my desire to own a modern game is fairly limited. There is something special about the feeling of making a trip to a location and running into some of your pinball friends there, too. What money I do have usually goes towards traveling to pinball shows and tournaments, anyway. Those are more valuable to me than owning a single game or two. With the games that we have on location in town, I probably manage to play more pinball than most of the people on this site, even the ones who have awesome collections.
I have thought about buying one DMD game and trading it for a new game every two months or so, just to fill in the cracks in my game knowledge. However, I've never actually gone through with that plan as I am not really sure that I want the distraction of having a game at home.