At the August meeting of Arlington's Bicycle Advisory Council, there was a discussion of the legal right of cyclists to the bike lane. Lindsay Brooker, the Commonwealth's Attorney was there, and according to her
There doesn’t seem to be anything in the Arlington Code that specifically grants right of way to bicyclists in a bike lane.
Where the County Board has by ordinance designated a bicycle lane for the exclusive use of bicycles, a motor vehicle may cross a bicycle lane for the purpose of entering or exiting adjacent property, for making a turn, or for the purpose of parking, but no person shall stop, stand or park a motor vehicle in a bicycle lane, nor shall any person drive a motor vehicle in a bicycle lane for a distance of more than one hundred (100) feet.
But it doesn't appear to me that there is any fine for driving in a bicycle lane (or even parking). This was the case in DC until a few years ago. The Arlington BAC is going to work with the CA to come up with better language, but I don't know if this will include a fine.
Speaking of Arlington bike lanes, here's they're short term plan for painting more.