I've found that driving about 15 mph over the speed limit seems to avoid a lot of encounters. Most people don't want to go more than 5-10 mph over the speed limit, so they generally don't try to keep up with me. And the ones that do keep up often want to go faster than 15 mph over, so I let them pass me.
Or just find some turns, like Rusty says. It's amazing how many Porsche drivers I've seen fly past me on the highway only to get stuck behind them going agonizingly slow on the curved exit ramp (and I'm in my wife's Accord!)
