Just took ours on the highway for the first prolonged time (from RI to NJ and back again). He rolls along at 70 quite easily. When you hit an uphill, you definitely have to press harder on the gas and you can hear the engine grow louder, but he makes it up the hills okay.
It was a bit windy (gusting to 25MPH maybe), but nothing too obnoxious.
P.S.: Avoid NY highways. Specifically, Route 287 from 95 to the Tappan Zee Bridge. OMG, what a horrible stretch of road for a Smart car. We hit two different potholes so hard I thought the car would shatter...