This is a handy yet simple tutorial that demonstrates the use of cloning.

power lines

From the articles intro:

This tutorial will teach you how to remove those annyoing powerlines while leaving the original image un-touched. I have to say I find myself using this removal technique on many landscape images, very usefull indeed. This techiniaue takes about 10 minutes to completey remove any traces of powerlines, but again it depends on the amount of lines

Cick here to view the tutorial