To the best of my knowledge, the main impact is on people's thinking. When motorists are made tangibly aware that the area they're driving in is intended by the designers to be used by both cars and bikes, they're more likely to behave like the area they're driving in is intended to be used by both cars and bikes. Does that actually work? I have no idea, but it costs almost nothing to implement, and I'd be shocked if it had negative effects.
Edit - Here's a quick US DoT summary:
http://www.fhwa.dot.gov/publications...0044/10044.pdf