Interesting question. I can't answer it directly, but I can tell you that most of the power is used for acceleration - that's what makes the hybrid concept work.
If I look at my mpg gauge while accelerating on to a freeway, for instance, it will be down around 10-15 mpg, but when I'm cruising on the flat, it will be around 75. So a first guess would be that 70 mph, something under 20% of the Insight's full power (67 HP, IRRC) is used to overcome friction from drivetrain, rolling resistance from tires, and air resistance.
If I look at my mpg gauge while accelerating on to a freeway, for instance, it will be down around 10-15 mpg, but when I'm cruising on the flat, it will be around 75. So a first guess would be that 70 mph, something under 20% of the Insight's full power (67 HP, IRRC) is used to overcome friction from drivetrain, rolling resistance from tires, and air resistance.