Also - does anyone have an install over IH2 that has the zoom function working?

I just uninstalled the easy rollover add-on, and the broken image problem has gone away but nothing happens when I mouse over the image. I have all the options in the Admin > Config > Images set to enable the image zoom, but nothing.

Problem is, I'm not even sure what it is I'm supposed to be seeing! What does the 'zoom' thing do, exactly?