I use Unix all the time. The OSX operating system used on all Macintoshes is built on it. I have delved into the command line interface (CLI) some, but not too deeply. It certainly is powerful, with a lot of specific, powerful utilities to do just about anything you can imagine. Even the command line itself is a powerful utility, with many different "flavors". 'bash' (Bourne Again SHell) is the default CLI, but it is entirely possible to use the C Shell, or Korn.
I use Unix at my job allot. We use AIX which is IBM's implementation of it. We use Korn shell on all of our systems. I have used the bourne shell in Linux and prefer the Korn shell, but that most likely due to comfort level from longer usage. I have never actually used anything but command line in Unix before, our systems have to perform for hospitals so its not even installed.
I think the hardest concept to grasp when moving from Windows or VMS is the Nested Filesystem. Its difficult to explain, but I will if there is a desire for it.