I understand this concern. It's like the old 20 Newsgroups data set for testing classification, where supposedly you're distinguishing the topics of conversatio

I understand this concern. It's like the old 20 Newsgroups data set for testing classification, where supposedly you're distinguishing the topics of conversation between comp.graphics, sci.electronics, talk.politics.misc, and so on... ...but what the most effective classifiers do is memorize the names and signature blocks of people who posted in each newsgroup.