Basically the whole post can be summed up via these choice quotes:

Overall, I disagree with his title, but I don’t disagree with his results ... his methodology, it’s mostly fine

Guy tested partial SPDY page loads, not full SPDY page loads. More specifically, he tested this case: if you upgrade your primary domain, but few of your other domains, your CDN, etc, how does SPDY perform?

(followed up with a table showing that this is a very realistic test scenario)