I have almost left with posting technical stuff on this blog. But yesterday I got one great plug-in in Firefox customized for Google, they called it Customized Google - . It has lots and lots of features but the most existing one is to put filter on Google search. Great to see they have made the complete regular expression algo in Filtering.
So, if searching book you don't want to see the face of the sites who sell books like Amazon. Go into the filter option add: http://amazon.com/*.
In the docs search if you are only looking for pdf docs not ppt docs, put a filter http://*.ppt(I am just assuming, I am writing it correct).
You can also block virus containing sites if you know the name or even guess the string of it. For any sub-page block, write like http://sitename.com/*.
I mean, you know how much one can play with regular expression. So, go ahead and block the crappy things for you. Great news is there is no effect on response time of search. Great going guys !