I have exceeded Vne in a Citabria attempting an inverted flight maneuver. Turns out, in the Citabria I was flying, the stick's forward travel is limited by the back seat stick hitting the back of the pilot's seat, if the pilot's seat isn't adjusted all the way forward. Nose drops. Airspeed climbs rapidly. Lesson learned. I was fine. I got the aircraft inspected by a mechanic, and there was no damage, but it was a bad situation. I'll let you get Ron's take on exceedances, but the limits are there because someone figured out that if you exceed them by a large enough amount you're going to break something and possibly die. We're not telling you how much is "large enough," because we don't know. Good luck.
Many students find the act of updating a flight plan en route to calculate estimated arrival times and fuel burns to be a little antiquated. And if you don't need to arrive at any particular time, and you're carrying more than 40% of your required fuel in reserve, then you're probably right. So while you might be able to skip it flying to lunch in your Cessna, these skills are actually still used in professional aviation. Read on for more.