If you want to learn Linux or Unix and you've installed Ubuntu, you've already gone down the road to not actually learning either one at all. Hell even OS X is based on BSD (Unix) and nobody who is an "expert" in OS X is ever considered an expert in Linux or Unix. There's nothing sadder than seeing a "Linux expert" try to use sudo on Solaris because they actually don't know a damn thing about Linux (seriously have seen this), because they're an Ubuntu expert, not a Linux expert.
Want to really learn Linux? Install Slackware. Want to learn Unix? Install OpenBSD, NetBSD, or FreeBSD. Want to pretend you're more knowledgeable about a subject than you are? Install Ubuntu. Now I'm not shitting on people who want to learn, just trying to steer you guys back on track. Your Ubuntu knowledge is literally applicable to no where else but Ubuntu. Now tell me how much being a Mandrake (like Ubuntu of the late 90s) expert means to the world today? Exactly. Don't get caught up in the fad.