I do it in my truck as well as the bike.
Often, cars will sit behind the straight going traffic, even though there is about 10 feet of space to turn. Rather than wait for the green light, I'll just head on through. About half the time, the car that was waiting will follow me through once they see that there is enough room.
As far as the legality of it: I think it is legal if nobody has their turn signal on. I have been told by traffic school teachers as well as current Highway Patrol officers that it is OK to pass a car blocking traffic as long as you don't leave the "traveled roadway", so just don't drop a tire off the pavement.
If someone has their right turn signal on, passing them on the right would be illegal.