I found an article that encourages bikers to take over the entire lane while riding and here were their reasons:

• Sidewalk – While the odds of you getting hit from behind diminish greatly, there are other dangers that come into play.
◦ Drivers are not looking for fast moving objects on the sidewalks so when you come to a cross street there is a good chance you’ll get hit by a turning car.
◦ Sidewalks are available for pedestrians and, in many states, it’s illegal for bicycles to ride on them.
◦ You are forced to (and should) go extremely slow. Besides dealing with turning cars and pedestrians, you are riding are surfaces that are not maintained for traffic and often have other obstacles to deal with.
• The extreme right side of the road – In my opinion this is the most dangerous place you can ride. You are risking two dangers:
◦ Cars will repeatedly try to squeeze by you in the same lane and will almost always come very close to you which, obviously, increases your chance of getting hit.
◦ The Peek-a-boo bike. Picture two cars approaching. The second car is following closely to the first. As the first car moves to miss you, it is seen by the second car as merely drifting in the lane since the car isn’t moving that much out of the way. The second car doesn’t realize you are in the road until it is to late.
Because of the above dangers and contrary to many people’s “common sense”, the best thing for a bike commuter to do is claim the lane. I ride at least a third of the way into the lane and, around curves, I roll right down the middle.

http://www.commutebybike.com/2008/03/18/to…d-why-its-safer

Now, Denver enforces no sidewalk riding, but at the same time, they state that you should ride where cars can pass you at all times, bringing attention to the second danger:

Sec. 54-572. Riding on roadways.
(a) Every person operating a bicycle or electrical assisted bicycle upon a roadway shall ride as near to the right-hand side of the roadway as judged safe by the bicyclist to facilitate the movement of such overtaking vehicles unless other conditions make it unsafe to do so.

So this really puts riders between a few ton moving metal rock and a piece of shit ticket…

one of the bigest things though was advice from the local police – ignore the bit of the law that requires you to ride as far over in your lane as “safe” and ride in the middle it forces drivers to treat you like a car and over take properly not squeeze round you, it makes you easier to see at intersections and gives you more room to avoid the bonnet of the car creeping out in front for a better view who very often CAN’T see you hurtling along beside all those parked cars. i’ve cycled round city centres including round the A40 in central london with a 60mph limit, twin carriage ways, serrious quantitiesof traffic and concrete walls either side and the big thing to remember is you have every right to be there, don’t be intimidated – and i know its easy when you’ve got 60 tons of articulaated truck doing 50 beside you and wanting to pull over – and dont give drivers the oportunity to cause you problems. most -but not all – acidents happen because people are being dumb or panic.

on a complete aside anyoneknow where round denver i can hire a (decent) bike andsome reasonable trails for a day at the end of themonth when i’m over?

However, I disagree with not riding on streets such as 13th Ave, 14th Ave., Colo. Blvd, Colfax, etc. I have had far more encounters with impatient drivers on 16th, 12th and other streets with bike lanes, or sharrows. Narrow side streets are just as dangerous (if not more) than wide lanes with speed limits under 40 MPH. Having large vehicles try to fit around me and between an oncoming vehicle on narrow streets is nerve racking.

The issue is impatience. Extend courtesy to others as you would like to receive it. That goes for not running red lights or stop signs!