Ouch
John,
I hate to say it, but I am owed a total of thousands of dollars from a variety of projects over the past 8+ years. Like you, I never publicly "outed" the companies in question. I do admit to private discussions with some other freelancers though.
In some cases you can consult a collection agency, but with your sum of money it probably isn't worth it. The agency usually claims about 20% of what they finally collect (sometimes higher when it is smaller amounts). It is a hassle, but this did work for me in a complicated situation when one company bought another, and then sold "assets" off to a third company. In that case I also paid a legal consultant so in the end I collected about 60% of what I was owed, but as I was owed $2,200 it was significantly more than $0.
Last year I spoke to the owner of one company in person while at GenCon, and stood there with him while he wrote the check.
Efforts to collect CAN pay off, but more often than not, if a company isn't paying, they just aren't paying. Some companies do have a reputation for paying slowly. When you are dealing with smaller sums of money, the hassle to try to collect tends to be less and less worth it. Every year at tax time I review the contracts that I still haven't been paid for. I get furious each and every time.
As someone starting my own .pdf company, I have made an effort to insure I pay people on time (or early as I still don't have releases ready). This is due to my own experiences of not being paid. My motto is, "I pay like crap, but at least I'll pay you!"
Good luck,
Patrick