Great question.
We've got a real mix on SmartPlanet. (For the record, you can see anyone's background by clicking on the "Full Bio" link in the biography box at the end of any article.)
Most have a background in journalism because that's the primarily task here, but several have technical backgrounds. (For example, the lovely Janet Fang works in the lab at the Lamont-Doherty Earth Observatory in New York. And the wonderful Sun Joo Kim is a practicing architect in Boston.)
Many others straddle the line -- they may not have technical backgrounds, but they've worked for publications such as Scientific American or Popular Mechanics or similar. When I assign writers to beats, I try to emphasize their strengths and interests.
