I'm far, far more impressed than Jon Hamm does. I've been a techie all my life, and I would walk straight past Linus if I saw him on the street. I only have a very vague idea of what he looks like.
And why should it otherwise? He's famous for what he's done, not who he is.
I'm mildly disappointed in RD Jr... he had so much geek cred after playing an awesome Iron Man, but I guess that's why it's called acting.