Castle Rock Entertainment, Inc. v. Carol Publishing Group, Inc.
150 F.3d 132 (2d Cir. 1998) - full text opinion
Seinfeld set the record for the largest number of viewers for a television comedy, over 108 million by the show's end. Even today, almost a decade after the final episode, the release of the first three episodes of Seinfeld on DVD sold around 4 million copies, more than any other TV show, ever.
Even though Castle Rock won its case, and had all un-sold copies of the Seinfeld Aptitude Test destroyed, it is still available for sale. However, there are plenty of other places to look for Seinfeld trivia. If you're unfamiliar with the show, the SeinFAQ is an excellent place to start learning.
This case is not the only time something Seinfeld related ended up in court. In Mackenzie v. Miller Brewing Co. an employee, Jerold Mackenzie, was fired for sexual harassment after discussing the details of a particular Seinfeld episode, "The Junior Mint," with a co-worker. He sued and was initially awarded $26 million by a jury, but this was overturned on appeal, and the reversal affirmed by the Wisconsin Supreme Court. Eventually, the plaintiff settled out of court for $625,000.