[MTrenk]

I don't believe that bumps would work. Dimples create low pressure zones that keep the boundary layer attached for as long as possible. Bumps won't really create that effect.

aerohead:
I know about the Reynold's numbers and blah blah blah.
--> A flat panel will have a short laminar attached boundary layer, then an attached turbulent layer, then lose any attached flow.
--> A dimpled (flat) panel will keep the attached turbulent flow, reducing drag compared to the flat panel.
Sure things are different based on how big your object is vs. how large your dimples are and stuff, but in no way can you say that a flat panel will be the same as a dimpled panel.

Still the best way is to not have a flat panel; an airfoil shaped bottom is ideal.