Hanson being pro-singularity is such a high-probability prior, it contributes nothing to anyone's estimate of the likelihood of a singularity. And, surely enough, his arguments are the same as usual: Moor's law, planes vs. birds, leave out the details etc.
Personally, I like the smbc take on the Moor's law (very mildly NSFW).
On a semi-related note, I envy you taking a course from Scott Aaronson :)
"Of course he would argue for X, therefore you shouldn't listen to his arguments for X" is a fully general counterargument. The fact that he is making arguments for X shouldn't cause much updating; the content of those arguments may very well. I realize that's not precisely the point you are making.
If the arguments are already known to us, then they shouldn't cause any updating if we are perfect logicians. However, it should be noted that this wasn't a general post on the likelihood of the singularity, but a response to the other article (the ...
Here's a great article by Paul Allen about why the singularity won't happen anytime soon. Basically a lot of the things we do are just not amenable to awesome looking exponential graphs.