This is not quite complete as far as explaining the reasons why he didn't accept.<p>The key quote can be found in the New Yorker article<p><a href="http://www.newyorker.com/magazine/2006/08/28/manifold-destiny" rel="nofollow">http://www.newyorker.com/magazine/2006/08/28/manifold-destin...</a><p>(someone else already posted it):<p><pre><code> As for Yau, Perelman said, “I can’t say I’m outraged.
Other people do worse. Of course, there are many
mathematicians who are more or less honest. But
almost all of them are conformists. They are more
or less honest, but they tolerate those who are not
honest.”
</code></pre>
He was disillusioned with the mathematics community not just with Cao and Zhu's dishonesty. It was more crushing and dissapointing that others didn't rise up to speak against it.
For those interested there is a good Russian documentary on Perelman's life:
<a href="https://www.youtube.com/watch?v=Ng1W2KUHI2s" rel="nofollow">https://www.youtube.com/watch?v=Ng1W2KUHI2s</a>
The New Yorker also published an excellent piece on Perelman and the solving of the Poincaré back in 2006: <a href="http://www.newyorker.com/magazine/2006/08/28/manifold-destiny" rel="nofollow">http://www.newyorker.com/magazine/2006/08/28/manifold-destin...</a><p>It's interesting to see the political implications behind breakthroughs like this.
Here is some info and a great explanatory video for William Thurston's geometrization conjecture, which laid down some of the work for the proof: <a href="http://terrytao.wordpress.com/2012/08/22/bill-thurston/" rel="nofollow">http://terrytao.wordpress.com/2012/08/22/bill-thurston/</a>
A quibble with the author's impression of peer review:<p><i>As we know, the process of submitting to a scientific journal has, besides the diffusion of one’s results to the community, the aim of verifying those results. Here, such an approach was made impossible by Perelman, so some independent groups of scholars set at the highly difficult task to understand, complete, verify, and explain his work.</i><p>Peer review does not "verify results"; peer review is there to make sure there are no serious and obvious flaws. Duplication of studies and collection of additional data / use of other techniques is what verifies results.<p>It is possible Perelman's papers received a more rigorous review because they were not peer reviewed – giving people incentive to dig into the details, perhaps more than they would have if the papers had appeared in a journal. But, given the signficance of the problem he was attacking, I suspect the papers not being in a peer-reviewed journal made little difference, in terms of how much effort was expended to check his proofs.