Why don't satellites and spacecraft collide in orbit?

[r.vittalkiran]

How will the space vehicles avoid satellites and those kind of things, when they are on a journey? I haven't seen any shuttle hitting a satellite/ even satellite(not geostationary) colliding on each other?
What's the reason of it not happening?

 

[Borek]

Most of the objects with size large enough to be dangerous are cataloged, and whenever there is a risk of collision, they are evaded.

Satellites do collide.

http://en.wikipedia.org/wiki/2009_satellite_collision