I say the following as a Linux enthusiast: Ubuntu is absolutely not "ready for the prime time," as you put it.
It's not ready for home users, it's not ready for most businesses, it's not ready for anyone except a small number of users.
It's not ready for home users, it's not ready for most businesses, it's not ready for anyone except a small number of users.
Audio still doesn't work on my installation. It can work if I kill Flash or pulseaudio---sometimes---or if I restart my browser or entire machine---sometimes. But it's an atrocious state of affairs to expect end-users to debug basic functionality like that, and they end up having to because there isn't a "Geek Squad" local-service ecosystem to take a malfunctioning Linux machine to (with your own customized distro install) where they can just "make it work."
It's not just a software problem---it's an ecosystem problem. Both in terms of the service / support sector and in terms of the software creation sector (the fact that there isn't just one answer to "How do I do audio on Linux" is absolutely maddening to someone used to writing software on a Mac / Win monoculture [http://braid-game.com/news/2008/08/misc-linux-questions/]).
I'm sure the argument will come that most home users only need a web browser, so the software selection isn't a problem, but at that point you might as well just use Chrome OS and get something that actually works.
Once it gets increased adoption more niche and paid for software will naturally migrate.
I say this as a Linux hating Windows lover who lasted 3 hours before reverting Win 10 back to 8.1 on my gaming machine and changing my wifi password, and I plan to never go to Win 10 or any Windows products again.