The standard rule of thumb for the last few years is that Linux is about one percent of the market - a myth that Caitlyn Martin debunks:
Linux and UNIX have held a majority share of the server room for over a decade. Linux is very competitive in embedded devices. It is also making great strides on the consumer and business desktop, which includes laptops, notebooks and netbooks.
Let's start with netbooks, the area where Linux has made the biggest inroads. According to ABI Research Linux regained 32% of the netbook market in 2009 despite being next to impossible to find in brick and mortar stores...
If you're still stuck with that one Windows app, WINE is a decent workaround, and Some tweaks to make WINE - the software that lets you run Windows applications in Linux - look nicer.
Is Linux without rebooting a good thing?
And what to do with a decommissioned touch screen voting machine: Make it a Pac Man game.