I'm going to have to agree with the majority that if there are separate bike lanes and sidewalks then each group should respect their areas.

There's a great example of what happens when you don't in the city of Thessaloniki here in Greece where the mayor built a bike lane all along the seafront which already had a relatively large sidewalk. The bike lane was lowered a inch below the sidewalk area and paved with asphalt for better traction, and is clearly distinguishable as a bike path, taking up only one fifth of the total sidewalk. Within a week of finishing of the project, the bike path was totally taken over first by joggers/runners and then by pedestrians, mostly women with strollers stating that the surface was smoother than the sidewalk tiles. It's reached a point where there's even a campaign to ban cyclist from the sidewalk and bike path because of recent accidents involving strollers and have them cycle on a narrow busy street which always has bumper-to-bumper traffic!

I can understand when there's no sidewalk or it's condition is really bad and pedestrians (strollers, joggers and runners) have to use a bike lane, but there's no excuse hogging one up when there's a sidewalk available.