Here is an interesting case - Henry Mills v. Henry Mills. The younger Mr. Mills sued his father for the child support he never paid while he was still a child. I've always known that you can do this in theory, just never saw it actually done. Not only did he sue and win, he was awarded around $1000 in attorney's fees for a total of $13,000. He wasn't satisfied with this amount and appealled to get a higher amount of attorney's fees as well as interest on the child support that had not been paid for several years.
Also interesting is that although the trial court knew that the attorney was going to get 1/3 of any amount awarded, the judge only gave $1000 in fees. While on one hand this seems unfair - if the judge gave attorney fees as much as the attorney was taking - attorneys would simply start increasing the amount of the fees knowing they could pass it along to the defendants.
This is an interesting case for anyone who is really hurting financially now - and was not paid child support for years and years. If your ex has property or even a just a decent job - it might be worth your time to investigate further.