I think this varies quite a bit based on the area.
Where I live, we have bike lanes but the lance armstrong wanna-bes refuse to use them. They claim they are "held up" by slower ciclists, however it's somehow acceptable for them to hold up the roadways...
We have lots of 45mph 2-lane roads. Even the most lance armtrongiest ciclists cannot even come close to keeping up.
So, they "hold the lane", the ride in the very center. Once there's a line of 10-20 cars behind them, they start to pass.
So begins the process of zooming by the moronic ciclist, totally unaware of the danger he's creating for both himself and motorists.
Then... After 10-20 cars have passed the ciclist, we come up to a red light. What does the ciclist do? All the sudden he doesn't want to follow the rules of the road, and filters to the front of the red light just to hold everyone up all over again.
10-20 people with ~20 minutes added to their commute. 20 more minutes of pollution, traffic, and time all due to the moronic ciclists which only follow laws that benefit them and swap between being a car/ciclist/pedstrian on a whim.