All of this stuff differs depending on the states. I'm still trying to figure out why some guys are discussing Illinois law in this thread about a situation in Massachusetts.

Some states define bikes as vehicles and other states (california being one) don't. Some require anyone going slowly to pull over and let others pass, others only require that if you're going slower than your vehicle is capable of normally going (i.e. tractors and bikes going like 20mph plus aren't required to pull over when cars line up behind them because they are going their normal speed). Some have 3-foot clearance for passing rules, others don't. And so on...