Well, if you’re the subject of one of those lawsuits, my advice would be: Speak to a lawyer.
To my knowledge, just about every case in which the RIAA has taken action has been settled out of court, usually with a payment and a promise not to illegally download music ever again.
As far as i know, the first (and possibly still only?) RIAA case to actually go to a jury trial was the case of Jammie Thomas, a woman from Minnesota. She lost the case, as was ordered to pay over $200,000 to the RIAA. But just a few weeks ago, the judge from that trial declared a mistrial, saying that one of his jury instructions was an error of law, and that the case would have to be tried again, with new jury instructions.
I started a thread about the mistrial issue a couple of weeks ago, but no-one was interested enough to participate. There’s a story about the judge’s decision here.