I wanted to try gentoo and got a bit into the installation till I found out that I couldn't do a stage1 installation so I stopped. But I really found a lot of new stuff in that, especially in lowlevel configuration. But I don't think someone who's new to linux would notice most of those things as it's basic follow the guide and don't do anything else.
I'm using debian myself. It has a lot of autoconfiguration I think so I don't think it's really good in learning the insides of linux.
Now there's also a difference in knowing about the inner workings of linux which you'll see some stuff about with gentoo and know your way around as in being able to do stuff in it. Then I'd say any distro would be OK if you can take it from say command line only to a graphical 'desktop' if you need to do. That'll give you both command line skills as well, as graphical skills aren't needed since it's often intuitive.
But really I think you learn most is by wanting to do something and then do it. For example I wanted my wireless card to work and made it work in the process learning compiling from source and kernel compiling, about the kernel and modules, about text file configuration, about runlevels and the startup scripts, about workings of the internet, about the debian package tools and I think even more. It was the first thing I did and I think it's still the most important thing I did in it. It was all command line work and you'll need to learn that to use linux to the max without asking everytime you have to do something.
And you can't find a gentoo forum here because they have their own forums and www.gentoo.org
so no need to get one here as well.