first sorry, i did not submit the link to the trick :S
here it is :
http://www.xim.uni.cc//content/view/53/58/

i think no matter how hard u test the softwares, there will still be bugs
read the above trick for example, there is no way someone can think of it
and lot of testing, takes time, makes develpping softs slow
and it is expensive, a major problem for buisness or commercial softwares

good words hiddeninclouds...