I can't believe this thread. I was thinking about how to do this and implement it in a good/safe way a month ago. I told my wife about it and how I thought it was a great way to try out pins and have variety without having to shell out all kinds of money for them. It's especially cool if your limited on space, because now you can have a different game in the same spot every month. I even had the name picked out for it. I was going to call it the "PEP" Club (Pinball Exchange Program).
My idea (if possible) was to get 4-6 people in a general area together and get them to swap equal value machines around for 1 month at a time. SO, if I put up my South Park machine, then the other people in the club would put up a similar priced game. Say T2, RS, FT, Taxi, PZ and my SP for an example. So, I'd pass my game to a person while I get say, Taxi. I then have taxi for 1 month. Then I swap taxi to the next person in line while I get say, RS. I have RS for a month and then pass it along again while getting the next machine. 6 months later, I get South Park back. I could do the same thing with TF (although my wife would probably kill me as she loves it LOL). And that grouping could be say...AV, Xmen, MET, AC/DC, and ST. And so on.
It could be a lot of fun. The only down side is moving the pins around. That's a pain in the... no matter how you look at it. Of course, you need to do this with good/trust worthy people who you know take care of their machines and would inturn take even better care of another persons machine.