From this answer the way to zoom in/out of text in Gedit is by installing gedit-plugins, enabling the text size plugin and using Ctrl + Mouse scroll to zoom in/out.
This doesn't work in Gedit 3.4.1 on Ubuntu 12.04. There are no changes on the text size - either increase or decrease.
Ctrl + + doesn't work either and the only way is to select the menu directly in "View" -> "Increase/Decrease font size". To get the 'right' zoom, you will have to do this multiple times - for me it came to 8 times.
How can I get the keyboard shortcuts working? It's tiring and time wasting.
EDIT
Another interesting question (check the first comment): How to zoom in and out of text in Gedit?