Knoppix has many uses. Many use it as a GNU/Linux advocacy tool, for which it is well-suited, as it comes with the latest and greatest FOSS software, which can be readily demonstrated to potential users. Knoppix is also a great rescue CD. And Knoppix lets me take my desktop anywhere by letting me save my settings to a configuration file. I can load Knoppix on any computer, load my customized settings, and mount a USB storage device as the home directory, and voilà! there's my desktop.
Knoppix has near "auto-magical" hardware detection. I never found myself going to great lengths to get hardware working. The range of hardware supported in Knoppix is amazing. I regularly burn Knoppix CDs for friends who want to check GNU/Linux out, and they are always impressed by the ease with which their whole system is booted.
One of the strengths of Knoppix is that it comes with so much of the software one may need when using a desktop -- more than 900 installed software packages, comprising more than 2,000 executable user programs, utilities, and games. It comes with KDE v3.x as the standard desktop, with KOffice and the Konqueror Web browser. I like KDE because of its excellent usability features and superior development tools. Knoppix always features the latest and greatest KDE version available at the time of release.
Knoppix also includes OpenOffice.org, multimedia applications such as XMMS with MPEG video and MP3 support as well as the Ogg Vorbis audio player, Internet access tools such as KPPP and ISDN-utilities, the GIMP version 2.0 for graphics, various tools for data rescue and system repair, and network analysis and administration tools.
Knoppix bundles many programming languages, development tools, and libraries for software developers, which a plus for me as a software engineer.
If you need any software you think might be missing (rarely), you can go to the Web and download the latest Debian package of the software and install it. Once you save your configuration after installing the software, you never have to install it again. Just load Knoppix, load the configuration, and there you go.
Knoppix is just not a LiveCD distribution; it can also be installed on a computer's hard drive using a simple procedure. The latest versions of Knoppix come with a script called Knoppix-install that make it easy to load the entire operating system to the disk.
This distribution is also updated regularly. Even after an official release (Knoppix 3.7 is the latest), many revisions are released which contain updated software packages and support for new hardware.
Although Knoppix is my favorite desktop operating system, I have one reservation about it. With the mass of software it provides, Knoppix sometimes works poorly on older systems. Luckily this seems to be changing. With the recent announcement of that Knoppix will release two version, one a light CD and another a heavy DVD, my single reservation may disappear.