I've since seen him live in San Diego, and he had a great set.
10/25/10 Update: Here's me with Posehn and his fellow Mr. Show alum Scott Aukerman after they presented The Blob at the Silent Movie Theater:
Seth Rogen and Aziz Ansari are probably the funniest guys of their generation. Rogen popped onto my radar back when "Freaks and Geeks" first aired, and Aziz's $#!++iest Boombox Blast first let me know he was someone to keep an eye on.
This scene from the movie Observe and Report (language NSFW) has them facing off by exchanging the same insult back and forth. Their body language and energy levels contrast nicely, and I wanted to make it seem like Rogen is saying the first part of the insult on his side of the image in an angry way while Aziz is finishing it on the right side of the image almost silently (watch the video link to see what I mean).
Ok, that's enough links and swearing for now. It's hard to turn off the caricaturing part of my brain now that I've tapped into it, so I'll be posting more in the future.