Rand at SEOmoz shows his frustration with Yahoo paid reinclusion. He tells a story of a client who hired him to clean up his site after being banned from Yahoo. Rand's team did just that and after using paid Sitematch program for reinclusion, the site was denied. Rand posts his conversation with a Yahoo representative, where he shows that even though the site is cleaned up, Yahoo has it on a list that doesn't allow it to be reincluded. I tend to see these posts and complaints arise weekly in various SEO forums, so this is far from a one case situation.
They won't tell Rand if there are issues with the current site, all they can say is that the site does not "meet our [Yahoo] quality guidelines requirements." For the full effect of the "absurdity" in the conversation, read the entry.
So what does one do if they are in Rand's position? First try following the reinclusion tips Danny worked up back in June of 2005. If that fails, I have reported that a fairly unknown Yahoo Second Review Request form works wonders in getting sites reincluded into Yahoo.