Waste of money. Horrible at skimming and will blow your tank up with micro bubbles. It will skim a bit if it's perfectly adjusted but it constantly needs to be adjusted.
I have a new tank - started on 8/1/12. I was getting silt (for loss of a better word) floating on the surface. I bought one of these seemed to work ok - no more stuff on the surface but it never did foam and now my whole tank seems to be full of suspended microoparticulate matter. I've turned off the skimmer. Tomorrow I am going to do a partial water change and test the water. I was hoping to add a fish or two this week - but maybe not.