Gentoo has excellent documentation if you intend to install up from stage 3, as fedorarefugee says. Excellent documentation. Its pretty much cookbook in approach. But I don't recommend it for the casual user who may want to try this and try that. The apt-get approach used by Ubuntu and derivatives is extremely robust and also easy to use. Don't always see that combination.
Gentoo's roll-your-own approach means that you install everything yourself largely from source, compiling as you go, but in some cases you might install precompiled binaries. But the nightmare of "solving dependancies" isn't nearly as fiddly as one might think, since Gentoo's documentation is solid. You just walk down the checklist and do what the instructions say to do, and it gets done. And done right, I might add.
Gentoo is not for someone who wants to see how AbiWord works, compare it with something else (Openoffice), and then uninstall the one you don't like later on. Just ... don't bother. But it does allow you to install what you want, exactly what you want, and only what you want, with every binary compiled and optimized for your hardware and your kernel and your specifications.
Do this once and you'll really appreciate binary installers, repositories, apt-get, and liveCD distros.
I think Gentoo is great to play with in Virtualbox. Awesome place for Gentoo. You have your solid, stable, live Mint install. With Virtualbox. And Gentoo growing like a little baby inside it. Its like playing Spore, only Linux style. You get to watch your little baby grow bigger and stronger with your help and guidance until she is ready to reach out on her own and pipe X to a secondary monitor. It'll bring a tear to your eye when you realize you're a daddy, your little girl is all grown up now, and she wants to marry the Xbox.