Free, powerful, highly customizable, fast, diverse, and constantly developing--what more can you want in an operating system? Linux is definitely the operating of choice for power users and administrators alike.
The biggest factors that affect Linux's adoption rate is hardware support, and user experience. Granted, many distributions now ship with incredibly good GUIs, the core of the operating system still remains very much like it has always been. Although more and more devices ship with Linux as the OS of choice, Linux's market share remains tiny compared to that of Windows and even OS X (based on BSD).
I have a Linux machine at home, that I use for firewalling, file serving, and other things, but it doesn't have a GUI installed. This is primarily because all the box does is serve. It wasn't built to be a desktop machine. Service layers however, remain Linux's primary focus. To access the box, I terminal in using SSH from another machine. The machine can be entirely managed through the terminal.
The question of the day is: Do you use Linux/BSD with a graphics user interface?
Or do you use linux primarily for services?
Hardware support shouldn't be an issue to most people either; the only real issue would be the level of support for the latest graphic cards, but it's not as if you're going to be able to play most commercial games in Linux anyway. In fact, I have more faith in the stability of (even minimal) Linux drivers than in the crap some companies dare to ship without any QA review. Let's face it, most of the time it's stuff like drivers that makes your system misbehave and/or crash.
FreeBSD/OpenBSD I've never used as desktop, but at least FreeBSD should do quite well there too, with a bit of luck in hardware choice. Same goes for Solaris really, unless you have the luxury of running it on real Sun hardware of course...
Hardware support for alternative operating systems is often a matter of corporate interest and an economical and often also "political" issue rather than something that Linux (or *BSD) should be directly blamed for. If companies don't provide either drivers or tech specs for their products, it's going to be rather hard to make that hardware work no matter what OS you're in.
The only good thing windoze has is DirectX. I wish we could have better OpenGL / XServer.