Here is a story about how Ubuntu could replace Windows as the main operating system on a non-tech-savvy user's laptop. I think Linux, though perhaps lacking some essential software for business use is ready for every home.
How my wife switched completely to Ubuntu
It's been years since I've used Windows on my own computer. But my wife, well, that's a different story. She's not the kind of user who likes how "hard" is to use my machines running Debian or Arch.
So I had Windows installed for her on the home PC and on her laptop. I was constantly cleaning, re-installing, fighting viruses, etc. due to Windows' infamous weaknesses in these areas.
Well, a year ago, when she needed to travel to Buenos Aires for six months, I had Ubuntu 11.10 installed on her laptop alongside Windows, and asked her to see if she could use just Ubuntu, reassuring her that this way she wouldn't have to worry about getting it fixed because it wouldn't be able to break. Her basic needs for the laptop were Skype (to stay in touch), Gmail, Office documents (via LibreOffice), and browsing the internet.
She even managed (with my guidance) to install and configure Ekiga to use a local SIP provider and call home at "local" rates
Her whole time in Buenos Aires, she managed to use Ubuntu exclusively (save for Netflix, but that's no longer an issue)
When she finally returned home, she continued to use Ubuntu as her sole operating system, and I have already upgraded her to 12.04, and will soon upgrade to 12.10, which is what I have running on my own PC and which is awesome.
My wife only knows how to use computers, not how to set it up or anything (she's a biochemist, not a computer scientist). That's my job. I think this example shows that Ubuntu is easy enough to use and understand that if it came preinstalled on more consumer machines instead of Windows, it would fit in well with modern consumers' needs. It may even start to become a standard