Here is an idea Instead of lying to get your competitors banned from yahoo why not just make a better site than theirs? That is the whole point of competition. So some a**hole successfully got your site banned from yahoo. Why would you want to then turn around and get other people to do the same thing that pissed you off so much? Forget Yahoo anyways, everybody knows Google ranking is what's important. And there is no way your competitor can get you banned from Google since no one even reads the e-mails they get. If you focus on just hurting your competitors rather than actually making a quality site you will end up just like 90% of the people on this forum. Chasing your own tail, and lucky to make $100 in a month.
You can't expect Yahoo! to personally look over everything in details. Of course they messed up, but I'm sure they didn't bother going through all of the copyright information. You know, I'm guessing your site probably ripped some stuff off the other site. Yahoo! still indexes warez sites, so...
Sounds like bullshit to me. If your site was removed as a result of DMCA notification you have remedies under the law. The person filing the notification must provide specific details of the alleged infringement. The host is required to provide you with a copy of the notice. Suggesting that others file a DMCA notice to remove competitors' sites is irresponsible and demonstrates your own ignorance. Filing false claims is against the law. Yahoo does a very thorough job when they have received a legitimate DMCA notice.