Theoretically, with all the e-mail that flows through its systems, Yahoo is in a really good position to spot and tag spam as spam. But if the screen shot below (taken today) is any evidence of how Yahoo is faring in the war, then it's time for another approach.
For example, we have Yahoo to thank for DomainKeys (an e-mail authentication specification). However, because Domain Keys is not a standard and not universally supported, Yahoo can hardly start refusing mail that doesn't comply with the Domain Keys specification. So, what good is it then? The same goes for other e-mail authentication technologies like SenderID from Microsoft or SPF. If Microsoft, AOL, Google, and Yahoo (MAGY -- pronounced "maggie") could settle on a handful of anti-spam standards that they'd universally support (and, at some well-publicized date off in the future, collectively refuse all non-compliant e-mail), I'm relatively certain you'd see a significant drop off in spam (as well as the false positives which, in reality, are actually more problematic to most of us than the spam itself).
There are plenty of people who think I'm wrong about this and they're very vocal about their own opinions in the Talkbacks to my many rants about spam here on ZDNet. Meanwhile, the problem keeps getting worse and worse. Talk is cheap. I've got an idea on the table. I've had it on the table for over five years now (ever since I started JamSpam). Clearly, nothing else has worked. Meanwhile, my approach hasn't even been tried. I just wish MAGY would give it a chance. If they need a forum in which to meet and hammer things out, I will be happy to host it. But, since nothing else is working and problem is only getting worse, I'm getting tired of hearing why working together can't work instead of what must happen for it to work.