Visualization of the 'Sans' font from GNOME Font Viewer.
Tech evangelist (and former Microsoft employee) Robert Scoble on why Linux has not yet conquered the desktop:

Name the #1 thing you look at most on your computer screen. For me it's the characters on the screen. If one OS has better looking characters than another (Windows Vista has a whole set of new fonts coming) then that OS will win with most users who aren't geeks.

This is the #1 reason why Linux hasn't seen any significant adoption on the desktop/laptop yet. [emphasis mine]

Of course. Linux's inability to become a major player in the computer market is not due to a combination of inferior hardware support (from sound cards to modems to iPods) and ignorance, but about fonts.

While I wish Linux could become dominant simply be investing more money in developing slick new fonts, I am pretty certain that it is not that simple (otherwise, bug #50529 could directly influence bug #1). While longtime readers of this website knows that Microsoft definitely considers fonts important, I doubt it is the forefront of the minds of non-technical users. ClearType impressed me, but it was not one of the reasons I considered when I was deciding whether to use Windows or Linux.

While Aqua might be the reason that some Apple diehards use OS X, Luna and ClearType are not what cause people to use Windows XP. Inertia is the primary factor here - Windows XP is preloaded on most computers today. By virtue of being "the default," Windows will always have an advantage in the computing market. In order for it to lose a significant portion of the market, Microsoft will have to make serious missteps.

People I know who are considering switching to Apple computers and Mac OS X are not interested in doing so because they dislike Microsoft, or because they adore Mac OS X visual interface. They believe that Mac OS X is impervious to viruses and spyware, andthat Apple's computers do not break. These fallacies are repeated in Apple's various marketing campaigns, and are thus absorbed by the public. Yet a majority of computer users still do not buy computers from Apple, because they imagine that switching to OS X would entail a substantial investment in time - an investment that they will be unwilling to make, unless they feel that they can no longer use Windows. If this tipping point is reached, I do not know whether it will be because of security issues like the Blaster worm, increased marketing by Apple, and even the advent of a super-userfriendly version of Linux, but it is clear to me that it will not be because of fonts.