WHether or not it is legal to take a lane (NOT on a highway--many highways don't even allow bikes on the shoulder) is totally dictated by local and state vehicle codes.

I know that oregon and california do allow it (and could get you the statute ## if anyone wants--they're on the SF Bike coalition and BTA websites), but not every state is the same here. So, if you're in a different state, you should probably check it out.

That said, i usually take as much of the lane as i feel is safe, on surface streets. SOmetime safer to take the lane (and not get doored), sometimes better to hug the curb.

I often feel that if i stand out some, i will be better seen than if i'm hiding in the shadows. I've never (knock on wood) been hit by a car because i'm in the lane, but i have been both doored and turned into by a car turning right and a car turning left during my urban biking over the years. I think if i was more in the lane, in each instance, i would have avoided contact with those cars.