Gedit 3.6.1, how to increase the number of recent files from its default of 5?

Using the dconf-editor, this value can be found in the schema under org.gnome.gedit.preferences.ui. The value that you want to change is called max.recents.

dconf-editor can be installed from USC here:

or from a command line using: sudo apt-get install dconf-tools

There exists as well a possibility to achieve this without installing additional software:

dconf write /org/gnome/gedit/preferences/ui/max-recents "uint32 10"

Or:

gsettings set org.gnome.gedit.preferences.ui max-recents "uint32 10"