I have owned my Insight since March 2011 and have driven 50,000 miles. I have averaged 41.3 MPG for the entire life of the car so far, which is what I expected and am very pleased. I have had to do nothing but 5 oil changes, air filter, cabin filter and one CVT trans fluid change as recommended. There have been no other issues with the vehicle. Tires are finally bald and will be replaced at 50K miles as well. Number don't lie though, I did the calculations and with the lower price and good fuel economy you would have to own the Prius for 7-8 years before it would start saving you money over the Insight.
Driving using the MPG light colored system is actually more then a gimmick. The Prius tends to get you 45 MPG and you just drive the car (at a higher price) however the Insight you must learn how to apply the appropriate gas pedal pressure to get great MPG by keeping the colors green on the screen. Really works and it teaches you how to drive your other car that may not have this feature. Car also drives better then people seem to think and I never felt like the car couldn't steer out of the way or handel a winding road, however immediate acceleration is lacking.
Backseat is too too Small! If you are over 6 feet tall your head will hit roof and you cannot even slouch down to avoid this because there is no leg room either. Fabric in the car tends to get dirty very quickly and has a funny odor, not bad odor just funny. Also Paint and Body Intergrity are poor, it takes barely anything hitting the car to cause a chip, scratch, or dent. All this being said; if you are looking for a car that can carry 2 people comfortably at 40 MPG for a $20K price tag, I really think it is a good buy. Just don't buy the car because you think it is better then the rest, this car does everything average nothing is outstanding except the price!