In the three years I have been using Linux as my primary operating system I've taken note that in general there are four different types of Linux users. Each one fits a distinct niche and it is possible to change from one type into another over time.
The Computer User:
This is a person that feels no emotional ties to FOSS/Linux. The computer is a tool to get the job done and they use Linux because it is the best tool for the job they are trying to accomplish. If Windows or OSX was better suited for the task, then they would be using that instead. They may have no idea of what FOSS or Linux is, they just know their computer works when they need it to. Odds are Linux was installed on their system by friend or relative who is a Linux Advocate or FOSS Extremist who was tried of fixing issues that kept popping up on Windows.
The Dual Booter:
Typically someone who has some computer savvy about them. Odds are they decided to give Linux a try because they just caught an interesting article about a shiny new distro release on Digg or because they know a Linux Advocate who recommended it. They might make a forum post or two to try and solve an issue they are having, but odds are if the distro doesn't "just work" they will start going on about how Linux "isn't ready for the average user" or "will never make it as a desktop operating system". If their Linux install does work, they still keep Windows around because they are a "gamer" or because they need to use a piece of Windows software that does not have a decent FOSS/Linux alternative as of yet.
Someone who uses Linux because they feel it is a superior or more stable operating environment. Typically this is someone who knows their way around the computer a bit and isn't afraid to post on a forum asking a question or get their hands dirty with a bit of terminal code to get their system up and running. While they love the power of FOSS they realize at the same time that the entire world does not work in this manner (although it would be great if it did). They are typically willing to use restricted codecs and closed source video drivers to get the performance and functionality they need out of their system. While it is not uncommon for them to recommend Linux to their family and friends, most times they will even help them get it setup, they realize that some people are happy with Windows and they acknowledge this.
They use Linux not only because it is fast and stable, but because it is FOSS. They view software that is closed source as something evil that must be conquered or changed for the good of man kind. The know the ins and outs of their system - most times for an FOSS Extremist the GUI is optional. If their hardware does not work right "out of the box" on their favorite distro they are willing to spend hours pouring over manuals and help pages to get it working. They almost constantly preach about the evils of Windows and Apple and take every chance they get to convert those they know to Linux or and FOSS operating system.
Do you think I covered most Linux users here? If not let me know other "types" of Linux users you think there are in the world. If I did cover them all where do you fit into my four different categories? Perhaps you are even a mix of two, personally I find myself somewhere inbetween FOSS Extremist and Linux Advocate depending on my mood.