People like me still see it as a geeky specialty. My assumption is that it isn't suitable for the average user without technical knowledge of linux. The increase of Netbooks with it installed will help to spread it. I may have a play with a low cost Linux netbook to see what all the fuss is about. My biggest worry with things like this is that they don't "just work" like OSX or sometimes Windows does.
I'm writing this from an Asus Eee PC 901 running Ubuntu Linux. It's easy as hell to get to grips with (unlike, say, Gentoo's installer or OpenBSD) but you do notice it's a freebie. I miss the attention to detail in the graphical quality of the UI, I do notice how despite KDE and GNOME's best efforts, there is a lack of 'cohesion' between individual app's interfaces.
Linux is great for what it is. A low-cost, lightweight OS that will easily do the job (and often a lot faster than OS X or Windows). The programs written for *nix are extremely well-written, on the whole, and what's more, they're free.
All of that being said, if OS X ran well on the Eee PC I'd install it in a heartbeat. Why? Because it's much more polished and a lot more welcoming to your average user. I don't need to know terminal commands, arguments and strings to run tasks quickly and easily in OS X, it comes with a nifty app called 'Automator' that works brilliantly and is very intuitive. I
can and on occasion do use the terminal in OS X, but rarely so. Linux is much more terminal-centric as an OS. Less-so with fuzzy-cuddly distros like Ubuntu and Mandriva, but there is still a strong terminal element.
That's not to say the Terminal is not a massively powerful and useful tool, but most people don't give a **** about it and will immediately be put off from using it unless they know what they're doing or theyh just want to play around.
It'll always be difficult to track Linux's market share. This is because there are so many variants of it using the same kernel, but also because it is (broadly speaking) not a retail OS (it is under the GNU public license, say 'Stallman' three times in front of a mirror, but there are many companies that retail their distros such as SuSE and Mandriva) and thus sales figures are largely non-existent. More to the point, Linux is so much more involved than other OS' out there. Microsoft and Apple have been pushing towards OS simplicity, intuitiveness and ease-of-use out-of-the-box since their inception, Linux has always seemed to be the polar opposite of that mantra, even when distros like Ubuntu are designed mainly for the market of cheap computer-illiterate users they retain a great deal of their bearded, socks-and-sandals heritage, and as such will always have a smaller user base.
Besides which, Linux is only on netbooks to keep overheads down on the units. Much cheaper to license Linux en masse than it is to license Windows and to pay for those silly little 'Designed for Windows...' stickers.