In Oregon, you are only required to use the bike lane 'if a hearing has been held and the bike lane has been declared safe'. Despite the fact that hearings of this nature have ever been held anywhere in the state, that hasn't stopped an appeals court judge in the 'Potter case' to declare that, since the bike lane was designed, approved and installed by the City Engineer, it is in fact 'safe' to use, and thus that all bicyclists are required to use the bike lane if one is present.
The cops are using this ruling to herd cyclists into the bike lane, even if the number of cyclists present exceeds the capacity of the bike lane, if the bike lane is in reality unsafe, or if other circumstances allow cyclists to 'take the lane', such as being able to keep up with traffic in the downtown area where signals are timed to 12-15 mph.
I have also on more than one occassion observed motorists honking / screaming at cyclists to use the bike lane in instances where they had left the bike lane either to turn left, or to get around obstructions (including stopped busses) in the bike lane.
Personally, I think that although bike lanes may work in suburban areas with long distances between intersections and no parked cars, in dense urban areas I think bike lanes create more of a hazard since there are parked vehicles adjacent to and/or vehicles turning across the bike lane at frequent intervals.