This is good news and seems to be the right way to deal with the problem of gratuitous suits while still maintaining the IP rights.
I don't think it is as huge as some have implied though. Incurring court costs isn't unheard of. What is significant is that if enough people publicly recoup their costs in suits it might inspire more to challenge the blackmail letters that are being sent. If enough people do challenge then the model that the RIAA has built will collapse.