siccome sul nuovo ubuntu 11.04 non andava più il comodo zoom, per ripristinarlo ho seguito questi suggerimenti

http://ubuntuforums.org/showthread.php?t=1762091&page=2

passo 0: installare CCSM

For anyone else experiencing this problem (assuming you have Compiz Config Settings Manager (CCSM) installed on your system), just do the following:

1. Open up CCSM.

2. Go to the Utility section (which is an option found on the left-hand pane of the CCSM window).

3. Open the Mouse position polling plugin settings page.

4. Set the Mouse Poll Interval to a value less than 10 (I set mine to ‘1’, and it works flawlessly).

If your Enhanced Zoom Plugin is not already enabled, you will have to enable it and manually set the shortcut keys/mouse buttons for the Zoom In and Zoom Out settings.

NOTE: For my system, Button4 worked for scrolling up/away from me (Zoom In), and Button5 worked for scrolling down/toward me (Zoom Out).

 

le configurazioni per me: