Learning Linux, music to my ears!
Most people think that installing Ubuntu now makes you a Jedi master of penguin force, but this is just the first step.
What you have to realize is that Linux is the most diverse OS out there. You can do ANYTHING with it, so, what is your interest?
Servers, gaming, GFX, programming, etc. or are you just looking at getting a solid general knowledge of Linux as a whole?
Begin by compiling your own custom kernel. You will be blown away once you see the power that is under the hood of this baby.
One of my friends at HP bragged that their new servers/AP had this encryption with that option to do this and that, and I just showed him the security section of the Linux kernel. Yup, they copied it straight from Linux. Linux had it all and then some.
Once you understand the kernel (kernel = Linux) and you can build a lean mean fighting kernel, then you can move over to another more challenging distro like Gentoo, Arch (not too fond of the manner in which they handle the kernel), Slackware, Sabayon, etc.