I've been a (with the exception of brief periods of insanity) full time desktop linux user since around 1998. So the things I look for in a desktop are much different than the things others might be looking for in a desktop.

I've been using Arch for a couple of years now and love it. However I would not suggest others use it. It's a great distribution, and I will not be changing, but I don't suggest distributions to people for a few very specific reasons:

  1. Distributions don't matter (sort of)
    Distributions, or the collection of software maintained by a group of people, 
    are not important, a distribution is, for the most part branding. Specifically
    branding of a particular feature (such as the package manager). If there is 
    well written documentation on the package manager for the most part you 
    will be fine. 

  2. Your desktop is not my desktop (or every year is the year of the linux
    desktop)    
    One thing linux advocates have missed is the fact that there is no linux desktop
    There is no great one size fits all scheme for everyone. What works for me
    breaks another user's desktop work flow. That is OKAY. 

  3. Software is what you really want. 
    Software is what you really want. Not Linux, but software. 

So you want to play around for a bit? Mess things up? Here are some suggestions for the "everything works" sickness:

Tweak: Find sysctl settings that you'd like to tweak

Here are some common ones:

vm.swappiness vm.vfs_cache_pressure

Documentation on sysctl variables is available in the linux kernel.

Find software to play with:

https://github.com/kahun/awesome-sysadmin

Automate your setup, use salt to do something cool (my configs are automatically pushed to my machines as soon as they are changed)

Use python, use perl, use php, setup a webserver at home.

BREAK STUFF AND MAKE TROUBLE. Feel free to ask for help under the #linux tag and I'll see if I can help.

Distro hopping gets more boring than actually playing with linux imo. So it's better to just break something and try to fix it.

You could also try: http://www.linuxfromscratch.org/