I spoke to Lyman's owner Kevin the other day about it and it sounds like a lot of fun: you can join a team or just be a guest player, and they set it up so you'll play with people of the same level as you. If you're awesome at pinball, you'll play others as good, but if you're a novice, you'll be with other novices. And you can win your own pinball machine, which sounds pretty great.
Registration is here and there's more info at FSPAzone.org.
The games are every Tuesday at 8:30 and guests and spectators are welcome too. If you haven't been, Lyman's is at 14th and Quincy, right next to the Red Derby, and is a great spot: relaxed, good vibe, and with tasty food. I'm a big fan of the pressed sandwiches with pulled pork, ham and jalapeños.