You might also consider trying out Arch Linux. (www.archlinux.org)

I moved to Arch after a few years with Ubuntu and I love it. It's a little higher-level than Gentoo in that you don't have to make your own file system or compile your own kernel, but it is an educational experience in that you have to install anything you'd like to use. When the 15 minute install is complete, all you have is a bash prompt. Getting a GUI, the ability to print, wireless, etc is all up to you.

They give you a great package manager and they maintain an excellent Wiki that can walk you through almost any task. Arch taught me loads about configuration.

Then again, I did Gentoo back in the day too. It might take 4 days to complete the installation, but you sure will learn some things! :D

Perhaps try it inside a VM. Installing gentoo from scratch is a brilliant way to learn linux, but it's not so much "trial and error" as "trial by error" (message.)

If you do it in a VM or on a spare machine then you will have convenient access to web resources, which you will need :)