It depends. 2 lane interstate, I'm in the right lane.
3 or more lanes it depends. I-95 in Georgia is 3 lanes the entire length of the state. Here, I'm definitely in the right lane also, unless I have to pass (which I rarely have to do).
3 or more lanes in an urban environment where there are numerous exits and entrances, and many fairly close together, I'm in the center lane. And in most urban areas the speed limit isn't 70 anyway. I know through the more built up area surrounding I-95 in Richmond, VA, the limit drops to 65, then to 60, and down town where the curves are a little sharper, down to 55. Riding in the center lane with the speed limit 65 or less, there is zero problem with that.