I've downloaded a copy of gOS on Thursday, and earlier today I burned it to a CD and tried it on my Vista laptop. All I can say is "Wow!". I couldn't get the wireless working out of the box because it doesn't include Network Manager by default, but it does appear to be available on the CD-ROM image (if not it'll be available from the Ubuntu repositories anyway), and it does specifically state that you need to use an ethernet connection anyway. As I wasn't going to install it, I was just trying it out, I wasn't able to use the internet with it, but it didn't matter as I'm familiar with the websites it has links for.
It looks absolutely amazing - it has a very clean,simple interface that's kind of reminiscent of OS X (though I'm not really familiar with OS X, having never used a Mac). For the average computer owner - ie. someone who will use it to browse the Internet, read e-mail, chat via IM and maybe write the odd letter from time to time, it's the ideal OS. The fact that it's based on Ubuntu means you've got access to all the apps in the Ubuntu repositories (and remember, Ubuntu has big repositories, only Debian has more), so you could potentially install just about anything available from there.
It is a shame that it has Rhythmbox installed by default - I'd have preferred Amarok, but I'll freely concede that although Amarok is an awesome media player, it's quite complex, and Rhythmbox is probably easier to use.
Overall, I'm very impressed. Although I'd consider myself a somewhat more technically advanced user than the target audience, I really like gOS. I showed it to other members of my family and they quite liked it too, though they aren't Linuxphiles like me. If I had a computer-illiterate friend or relative who wanted a computer, and this OS was available preinstalled on a computer here in the UK, I'd certainly recommend they get it.
The Internet has become a killer app for the home computer, and this computer is built around that idea. In the process it may have become the killer app for desktop Linux...