Here's why Microsoft has the perfect monopoly with Windows and home users – this will sound very cruel but it is true: Windows assumes the home user is dumb and makes everything easy for home users.  Here's a good example:
in Windows, you have a fully stealthing firewall enabled by default, but in Ubuntu you have to manually install a firewall AND manually edit a file (before.rules ) so that the firewall in Ubuntu passes the "Shields Up" test:
https://www.grc.com/x/ne.dll?bh0bkyd2

Things like parental controls are absent in Ubuntu and simple things are not included in the default install, such as "gnome-games".
Here's another frustrating issue: why doesn't Ubuntu alert the user that the "restricted extras" can be installed to use things like Flash Player, play mp3 files etc.?  I know Ubuntu can't legally include the restricted extras in the default installation, but why not TELL the user that they can install the restricted extras?

Another thing that home users are familiar with and Ubuntu doesn't seem to care about: the user interface.  Ever since Windows 95 – i.e. from about the time when people started using computers at home – Windows users have the familiarity of the single task bar at the bottom of the screen and it's been constant ever since.  In Ubuntu, you have the cumbersome "Unity" interface which frustrates users – it really does!  If Ubuntu were to see how much easier "Lubuntu" is for newcomers from Windows, instead of forcing users to learn the Unity interface, then Ubuntu would become MUCH more successful.  

I'm sorry if this message has sounded too critical, but it needs to be said and I would love to see more and more people use Ubuntu instead of Windows, but that won't happen until Ubuntu follows Microsoft's example of making everything very easy and always using the single "task bar" at the bottom of the screen like "Lubuntu" does.

Finally – this IS a killer for Ubuntu...
Users must upgrade the entire Ubuntu install just to: run newer programs, use newer hardware and still have their installed version of Ubuntu supported?  Upgrading Ubuntu can break things, such as power management, drivers for wireless or other hardware devices.  I have strongly suggested in the "Ubuntu Brainstorm" that there should be a "live" testing mode before upgrading, to see if the newer version of Ubuntu will work before the user upgrades Ubuntu AND I have urged the Ubuntu developers to make the installation "cleanly" install without affecting the /home directories.

This is where Microsoft wins again!  Look at Windows XP for example.  It was released in 2001 and it is *still* supported by Microsoft until April 2014: http://support.microsoft.com/lifecycle/?LN=en-gb&C2=1173

Users don't have to upgrade Windows just to use a newer versions of most programs, except for some newer games, which require Windows Vista or Windows 7.

I really wish I could print this whole comment and discuss it with the Ubuntu team and Mark Shuttleworth.  It would be BRILLIANT if more and more people used Ubuntu instead of Windows, but that won't happen until these problems are addressed.  To finish this comment, I must say the security in Ubuntu is excellent and more user-friendly than Windows i.e. in Ubuntu, you just need the right password, from the user who has sufficient privileges.