In the previous version of Ubuntu (eg: maverick, natty), I used to do a:
sudo apt-get install gedit-plugins seahorse
to have the ability to encrypt/decrypt file within Gedit after enabling the plugin in the preferences.
But since, Oneiric I've not found a way of achieving this.
And now that I'm running Precise (the LTS version!), I'm a bit disappointed of not being able to do such things.