Busy shoulderless 4 lanes should be avoided like the plague. Contrary to what some may say, a 20 mph bike on such a road can cause major backups if it is busy enough.

When it is necessary to use them, i like to take a good chunk of the lane, right tire track or better and then watch overtaking traffic like a hawk. A helmet mounted mirror in such conditions is essential, IMHO. If you spend half your time looking over your shoulder, something ahead of you is going to take you out sooner or later.

When riding in these circumstances, i will generally move to the right after i am confident that the overtaking cager has acknowledged my presence by moving over. it's kind of my way of acknowledging him back and thanking him for not buzzing or steamrolling me. i use these same tactics if it is a two lane road, although in that case I might be a little quicker to commence "gutter cowering" as my VC zealot friends like to call it.

If you do find yourself in a situation where it appears that a substantial amount of traffic is backing up due to them all having to merge left to overtake you, it's a good idea to look for a section of useable shoulder or maybe even just pull over and have a swig of water to let the log jam pass. Too often I hear "screw them, if they don't want to waste a few seconds waiting to pass a bike". Just remember it works both ways. We too should consider wasting a few seconds in the interest of 2/4 wheel harmony.