Wingtip vorticies can sit over a runway (or even drift over to parallel runways) for minutes after a takeoff. They are very dangerous to smaller aircrafts.

The key to avoiding vorticies is to take off at a point earlier than the previous aircraft and to climb at a steeper angle (vorticies travel behind and downwards from the aircraft that made them).

Example: http://www.boldmethod.com/images/learn-to-fly/aerodynamics/a...

Helicopters can also produce serious turbulence as well!