I like Michael K calls for what they are: a canvas, on which Tom can paint. An impossibly huge canvas that seems to stretch out forever and maybe there isn't enough paint in the whole world to fill it, maybe there hasn't ever been enough paint to fill it, on which Tom can paint.
There are a handful of regular callers with "gimmicks" who can make it work, and he's one of them. I think the worst thing most people can do is call in with a bit in mind, because it betrays the fact that you probably don't "get" the Show as well as you think and really know where the callers best fit in, but I firmly put Spike and Michael K in the camp of those who pull it off and Tom obviously knows their rhythms and when to dump them. As others have said, he clearly listens to the Show, is a fan and knows what role he's playing (sign of a good bad caller: someone who either knows enough to keep talking when Tom is giving them rope or is delusional enough to keep calling when Tom is giving them rope). It's fun, the right doses, to get mad about Michael K calls, is how I'd put it.
For almost everybody else, the ground rules should be to either call in on a topic or call in with a story/thing to ask Tom about and then pay attention enough to follow Tom's lead and/or get out of the way when it goes somewhere.
I would have bet that Joey Levels would never return if you asked me last week, but then Mr. T Guy magically appeared, so anything is possible.
