According to Ars technica, 11 Ohio State University students have hired their own expert witness to poke holes in the RIAA's case against them. The expert witness for the students (a computer networking and security consultant) pointed out several flaws in the technical aspects of the case, as well as "difficulties inherent in trying to sue an IP address, which is essentially what the RIAA does."
As the expert noted, many technologies exist and are used almost ubiquitously on large computer networks that mask the identity of a given user/computer combination. Similarly, because computers are shared so easily by many people, yet can use the same IP address for a considerable length of time, the RIAA's approach makes "beyond the shadow of a doubt" a hard standard to uphold.
While most actions brought by the RIAA are simply settled out of court, it appears that there may be an advantage to actually fighting the lawsuits for some students. For universities, on the other hand, it is unclear what ripple effect this may have, as the RIAA may need to pursue different avenues than the ex parte discovery approach if students are successfully fighting in court.