I've had the Insight for about three weeks now and I really do love it. Over the first 1,000 miles I've achieved an average of 51 miles per gallon without really trying. The only thing I've had to do differently is slow down from my pre-Insight speed of 75 on the highway. I live in the Midwest and my commute is not very hilly. At a speed of 65 MPH I am getting 50 MPG. I have not yet had to use the A/C or the heat, which I expect will bring down the numbers come summer and winter. The auto-stop feature is great on gas, but takes a while to get used to. The gas kicks back on when you release the brake and the result can be a jerky response at the line if you hit the gas too quickly.
The Eco-Assist functions are very helpful. The green glow on the dash when you are driving efficiently and all of the data the on-board computer gives you at your fingertips is really impressive. It feels sporty to drive vs. the Prius. Calculating what you are saving on gas is pretty fun too!
I was surprised it did not come with floormats or mirrors on the sun visors. I'm not crazy about the hatchback, which allows everyone to see what is in your trunk unless you cover it with a blanket. The trunk and back seat are not very roomy, especially compared to the rival Prius.