I have a little problem with the lane position theory being some kind of "rule". Where you should be in the lane varies depending on type of road, traffic, and weather conditions. The important thing is to use the whole lane accordingly. In rain conditions on a heavily travelled road, the water will be deeper (ponding) where the car tires run. Bikes can hydroplane too. On an interstate highway at 70 miles an hour, you can hug that center line if you wish, but an oncoming semi can push a whole bunch of air at you. And crosswinds can move you around a bit as well... In city traffic, stay as visible as possible, but assume no one sees you. They will pull in front of you, pull right in behind you and in some cases try to occupy the same space you are in.
So use the entire lane, keep your mind on what you're doing and don't make any sudden moves. You will eventually develope a "sixth sense" - that guy isn't going to stop/that girl behind me is on a cel phone and not paying attention/that truck driver doesn't know I'm back here/that minivan is going to pull out in front of me, etc. etc.
I rode up on a sidewalk once to avoid a jerk who ran a stop sign..... it happens. Keep your options open and you will lessen your chances of becoming a statistic.
