If I create a theme, can I export it for import later or for distribution?
By default you cannot export a theme. But there's a great little add-on that a couple guys wrote that you can find here: https://www.dropbox.com/s/31xmun35z15grcy/theme_export.py?v=1mci
It adds an "Export Theme" button to the bottom of the User Preferences > Theme section.
Open User Preferences, go to Themes, change stuff and then click on the plus symbol next to the theme selection button:
Next, type in a name for the file (without extension):
Click OK and you should be able to find the file (XML file, in this case "the_best_theme.xml") in one of the following folders (depending on operating system):
%APPDATA%\Blender Foundation\Blender\[YOUR VERSION]\scripts\presets\interface_theme\
/Users/$USER/Library/Application Support/Blender/[YOUR VERSION]/scripts/presets/interface_theme/
If it is not in one of them, it might be in the subdirectory
.../scripts/presets/interface_theme/ of some other configuration directory as descibed here: https://www.blender.org/manual/getting_started/installing/configuration/directories.html