I don't know how true this is? I have talked to someone who runs one of the bigger exit nodes and he said that he used to get barely one or two abuse complaints in months.
It seems that if you don't run the limited exit policy, you'll be hit with DMCAs pretty much instantly.
If you do run the limited exit policy, you'll get hit with abuse notifications (you hacked my site, you're posting spam, etc) pretty quickly.