Tested on Firefox 3/4 (sux on chrome, i won't adapt the exploit)
It's the same hack as the one for twitter, exactly the same code source, just used the google plus1 button instead.
Just move the mouse and click somewhere, you will automatically plus1 this page.
You need to be connected on your google account and have already plus1'd at least one website unless it will popup a window
If you never +1d before, go on http://serphacker.com/enable-plus1.html before clicking here