I'm not sure why the audio wasn't working for him, but it all worked great out of the box for me on my MBP. Even some obscure Flash video sites I tried out would send both audio and video up to the Chromecast device.
It is certainly an interesting product, I'm hoping for integration into video apps on the desktop (VLC please god). The news earlier this week about apps being disabled is a bit disheartening, though their TOS clearly states you can't distribute them.<p>It is clear that "slinging" content to your television is a direction we'll be heading.