SO here is what I do that works very well for me. I made a surface skimmer that I use when I do water changes. Its easy to make and doesn't cost much. Take two 90s end to end forming U shape. On one end you use your drain hose. ON the other end connect a tee. I made this one out of stuff I had laying around but any tee will work. When you do water changes just keep the top of the tee close to the surface and it sucks up the scum. The side part of the tee keeps the hose suction. It might take a couple of water changes to get it all cleaned up but this method has worked the best for me. Any small amounts left mollies seem to eat it. At lest in my tanks.
OH!! and it works for sucking up lady bugs off the water surface that seem to think my aquariums are swimming pools. I don't know about the rest of you but I get dozens of these things a week in my tanks.

update 2/25/05
Post by Ben C
That's cool Hawkeye, thanks.
Don't suppose you know the CAUSE as well do you??!!

In my case its a lack of surface turbulence. I could all so come form weak filtration of even lack of bacteria in the filter so there is a build up of protein in the tank.
Mollies are good for eating this scum off the surface too.

Hawk