How often are filibusters used? Why?

They are used to delay or block legislation someone does not like. They used to be rare, but are used more frequently now.

Read about it:

http://www.google.com/search?sourceid=navclient&aq=&oq=fili&ie=UTF-8&rlz=1T4VRHB_enUS648US649&q=filibuster&gs_l=hp..0.0i131l2j0j0i131j0.0.0.1.112960...........0._7Jg-6QuWsA