I've been using Ubuntu half a year now after ditching Windows 2000 (yes I know).

What I like about using Ubuntu:

- the fact that I can tweak and customize almost anything.
- installing and updating massive amounts of free software via the repositories
- no worries about spyware and viruses, or antivirus software hogging the memory
- managing windows with XFCE and Compiz-Fusion is much better than Vista
- the idea that it is MY software and no company dictating how I can or cannot use it.
- the Ubuntu forums and documentation are awesome. Much more helpful than MSDN. I could solve every problem I came across so far by searching them.

What I don't like:

- the fact that I *have* to tweak and customize to do simple things, like using multiple monitors.
- the hodgepodge of not so integrated applications and libraries that don't always work together
- buggy XGL, Flash plugin crashes Firefox all the time
- (Proprietary) driver issues. For example there is no decent driver yet for my ATI graphics card that works with the new kernel in Gutsy, so I'm stuck with Feisty
- no Adobe software available. Although the Gimp and Inkscape are nice.

I think you can get by with how-tos and copy-and-paste solutions from the forums, but like BoxOfSnoo wrote you can dig endlessly into the internals of Linux. A good place to start is getting familiar with stuff like basic GNU tools, bash scripting, rights management, the boot process, and how X works.