Here's the skinny about floss. The purpose of floss is simply to disrupt the matrix (skin) of plaque so that it can be washed away with saliva, and remove food that may be stuck at the junction of two teeth. Seeing as your toothbrush does not reach in between the teeth (unless you are using a Rotadent), they are cleaning two different areas. Timing is not nearly as important as technique, however many people have benefited from brushing first and then flossing before rinsing to help drive the paste under the gums and in between the teeth. Hope this helps!
Carrie, Registered Dental Hygienist, Natural Gumption Co-Owner