Opera has a particularly useful feature called FastForward, that let’s you navigate from one page to the next—like from a page of Google results to another—simply by hitting the space bar.

Ever since the upgrade to Opera 11, the shortcut appeared broken. It was only too easy to attribute it to the upgrade. But apparently the change seems to have occured at Google’s end. 

The fix outlined for Windows works reliably on the Mac as well. But there are slightly different steps to take:
Locate Opera.app. You should find it in your applications folder.
Right click and choose “Show package contents”.
Drill down. Contents >> Resources >> ui >> fastforward.ini
Put a copy of this file onto your Desktop.
Open it in a text editor of your choice.
Scroll down until you find a section labeled ;English.
Add " Next "=101 (with straight quotes and mind the spaces) under ;English
Save and move the file to ~/Library/Preferences/Opera Preferences/
Relaunch Opera.

FastForward on Google should work as expected now.