Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Imagine an Operating System that only includes the features that you actually want and use. An Operating System that is finely tuned to your computer hardware. One that doesn't include any resource hogging applications that you don't need such as "Desktop Search" or huge bloated software such as modern music players. A System that doesn't need to be re-installed or upgraded every 6-9 months like most Operating Systems. Well, if you are partial to Linux, Gentoo Linux is such an Operating System.
Gentoo Linux is what is referred to as a "Source Based Distribution". What this means is that you build all of the software that you will use directly from the "Source Code" - Source Code is what developers create and modify, mostly comprised of text files, however, computers don't understand Source Code. In order for a program to be usable on a computer, the source code needs to be compiled into Binaries (the "language" computers understand).
Since Gentoo Linux is built from source code, it is a highly configurable distribution. For instance, instead of building the source code to a generic 32 or 64 bit processor, you can tell the compiler to build the code specifically to your exact processor. This alone can give you a noticeable performance increase. As well as optimizing the binaries for your computer (cpu architecture), you can also optimize the software for the features that you want your software to have (and ignore the features you don't want to have).