Is anyone else annoyed that Ubuntu still can't play YouTube videos out the box?
 

Why not just make gnash part of the default install? Also why does the Kubuntu 9.10 live CD only have a firefox installer? Also, why do you have to enable Universe first in order to get it? Surely tyhere's a case for having such a popular and useful piece of software pre-installed?

You can't possibly direct associate YouTube with Ubuntu's functionality. You clearly have to draw the line at Flash support, and whilst I'm not that familiar with it, Gnash is still beta and if you bring up a browser for a non-technical user that only plays "most" flash files, that would probably look pretty crap, no? Flash appears to be installed, but it's rubbish. Super. Not a good advert.

Not if you are committed to using purely OpenSource, public license software. See ubuntu's philosophy.

And this isn't really a problem, since you only need to pop up the "Software Center" (used to be "Add/Remove" app) and grab Flash from there; pressing a button is pretty much all it takes. This is the place you are guided to, if you read the help provided. Of course one can argue that this is too complicated, but if it is, then why are we still using our computers and not having an assistant do it for us?

What OS can play YouTube out of the box? Windows can't, can OS X?

Some distributions ship with Adobe Flash, but I don't know the legality of that and as acid_kewpie said, Gnash just isn't a suitable replacement for Adobe Flash yet. Though I seem to remember one of the big distros shipping with Gnash, maybe Fedora?