I go the speed limit.
It drives Child crazy at times, but that's who I am. I prefer the casual, relaxed driving and letting people pass me to the tense, high-speed passing of other people.
On the Interstate, that means that I can usually be found in the either the far right lane (the slowest lane) or the far left lane (the carpool lane). Despite it being on the far left and usually having less traffic than the other lanes, that does not mean the carpool is the "fastest" lane.
The upshot and rant portion of this post is that if you come up behind me doing twenty miles-per-hour more than me and starting flashing your headlights, I'm probably not going to move over. If I'm in the far-right/slowest lane, there's nowhere for me to go. If I'm in the far-left/carpool lane, it's usually the same: most of the time there's a double-solid line and I'm not going to cross it, breaking the law so you can get on with your own breaking the law. Sorry. If I was going under the speed limit I might sympathize with your position, but I'm not, so I don't.
And just so you don't think I'm a jerk who loves to irritate people, the other day a truck pulling a trailer came up behind me on a hill while I was in the second lane and flashed his lights at me. I promptly moved over so he could keep his momentum. I'm not out to make your life miserable on purpose, I just have my own pace, I keep to the lane designated for people with my pace, and I don't like you trying to push me to a faster pace.
Enjoy the road!