The whole post basically said the author was stupid while neglecting to explicitly point out anything wrong with what he/she said. That's pretty much the definition of ad hominem, no?

Not at all. http://plover.net/~bonds/adhominem.html

As I said, insults are not ad hominem in and of themselves.

if insults don't make an argument ad hominem, what does?

"He's an asshole, but he makes a good point."

Not ad hominem, not trying to refute the argument, but still an insult.

"He's an asshole, and his argument is crap."

Not ad hominem, refuting the argument by mere assertion, and an insult.

"He's an asshole, so his argument can't be taken seriously."

Ad hominem - implying that some characteristic of the person makes his argument flawed; and an insult.

"He just wants what's best for his daughter, so his argument can't be taken seriously."

Ad hominem (implying bias); but not an insult.