Everyone knows that tailgating on the highway can increase your chances of an auto accident. You probably still remember as a student driver being told by your instructor to always make sure you can see the four wheels of the driver in front of you as a good reference for actuate separation. Well, very similarly airplanes flying too close to one another can be hazardous too. It can lead to wake turbulence & it can potentially cause an accident. Wake turbulence is not like regular turbulence. It has nothing to do with the weather. It's a byproduct of the airplanes lift. It's mechanical it nature because it's only created by the wing tip vortices of an airplane in flight, or just taking off. Every airplane creates it. Accidents are rare because pilots are well taught about the hazardous of wake from the time they are student pilots. Just like car drivers use reference points to ensure accurate car separation, pilots do the same. They use various techniques to ensure safety. For example, they note the takeoff point of the previous departure & avoid the aircraft's wake, they wait 2 minutes between departure for large aircraft which is also required by regulations. They turn on aircraft ignition just prior to takeoff to provide immediate relight of the engines incase of engine failure cause by the prior aircraft's wake. In many case's large jet's still encounter each other's wake on a day to day basis without incident. It doesn't mean that a plane will crash because of it. At best you might feel a light jolt after takeoff. It's not hazardous when aircraft of the same group category encounter each other's wake. For example, a B737, or MD-80 are in the same category as far as weight & size. However, a A380, or B747 are in a totally different size. They are heavy aircraft class that gross over 300,000 lbs. So, any smaller airplanes following behind an aircraft in this category better have a safe distance from this class of airplane. In addtion, air traffic controllers will constantly remind pilots when they are following large & heavy airplanes. Wake turbulence accidents are extremely rare. The last wake turbulence accident was in the mid-90's when a private corporate jet got too close to a B-757 on landing. The corporate jet crashed. Airline pilots are well trained in avoiding each others wake turbulence which is why accidents are rare. To learn more about wake turbulence I included a excellent video that talks about the basics.

http://www.youtube.com/watch?v=eyHg2g4wbG4