Gentoo Linux 2006.0
It's been a while since I last reviewed Gentoo Linux because there haven't been too many significant changes in the past few releases. I've been using it as my primary desktop operating system for a year and a half, though, and I've been running my main Web/email/database server on it since October of 2004. There's a reason why I've stayed with it that long, both as a desktop and server OS -- and there's also a reason why I'm writing a review of the 2006.0 release after a long hiatus from Gentoo reviews.
Gentoo Linux is a unique GNU/Linux distribution that compiles all of its software from source code rather than using precompiled binary packages. Gentoo is arranged much like FreeBSD, except it has command line tools that automate all of the special functions that must be done by hand in FreeBSD. Where FreeBSD has the Ports system, Gentoo has the automated Portage system; where FreeBSD has /etc/rc.conf to regulate boot processes, Gentoo has the rc-update tool to add or remove scripts from the startup process.
Although the entire system can be compiled from source (and updates are applied by recompiling the whole program), there are a few binary packages available for some of the larger applications, like OpenOffice.org and Mozilla. You can also install the operating system from a binary package, then recompile it as each piece of the operating environment needs updating.
The number of programs in Gentoo's Portage tree grows constantly.