This is very useful information, thank you. One concern though is that, from what I've read recently, a lot of the data brokers refuse to let citizens view their own records so I would be unable to know what they say about me.
I think the current state of things is that you'll receive a letter if someone does a check on you and in that letter they'll explain how to get a copy of the report. I could be wrong about the specifics on that, but that's how a lot of the states were doing it and I think it might be federal law by now.
It wouldn't hurt to call one of the big companies and just ask what it takes to see your report. (they might try to charge you for it. this is a bummer since different companies might not necessarily create the same report, depending on the quality of their database.) I think in the long run the industry is moving towards something like credit reports, where you can see yours for free periodically, but I don't think they're there yet.
They might also be moving towards getting rid of these big databases altogether (they get sued a lot for inaccurate results) and relying fully on sending runners to individual courts to get searches, but that doesn't scale well enough to cover the entire country every time you do a search on a person. The big databases that pull in records from state, county, muni, DOC, and so on have their problems but it's not hard to see why they came into existence: law enforcement and the courts are not properly centralized. My sense is that the industry is in a state of change but I don't know anything for sure (except that getting an expungement is one of those things you might as well try since taking the shot doesn't cost too much and it might help :) ).