For the most part, I ride the same as Tom explained. My ride to work is almost all 4 lane split highways. I almost always ride in the left lane, nearly on the center line.
I have found that in MN, if you ride about a foot or two to the left of the center line (on a four lane road), most cars actually move over to the right and give you more space. They get uncomfortable when the get next to a bike that is riding close to them. The also will rarely match your speed when you ride that way. Obviously not all cars will give you space, but I do find that most of them do. The louder pipes help too.
I think this spot makes me the most visable, and I can see the best. Here is a pic to demonstrate (notice the blue car is giving me space):
