I had never heard before of an older (40+) mathematician, who has done essentially no meaningful work in the subject before, and has virtually no publication record, coming out of seemingly nowhere and proving such a big theorem.
This is in no way a slight against older mathematicians, indeed many spectacular results are proved by people over 40, but they typically accumulate an excellent track record on the way.
Indeed, I fully assumed that this guy was full of shit. However, I have heard that well-known experts in the area have closely read Zhang's paper and found it to be correct.
This is enough to put a smile on my face. There is something wonderful about skepticism and cynicism being proven wrong, especially when the skepticism is my own.