Justin switched to Dolphin under GNOME because Nautilus was too slow at expanding directories and the like.
One annoying “feature” for him is that Dolphin uses single click by default. Normally a user could change this under System Settings, however this is not installed.
So, the easiest way to change this (probably even if you do have System Settings installed!) is to edit the configuration file in your home directly.
sudo vim ~/.kde/share/config/kdeglobals
[KDE] section, add
SingleClick=false and save.
Close and re-open Dolphin and everything is now double click again.. *Ahhhh*