Ad Hominem arguments do not deal with the facts, but rather attempt to discredit the person or entity presenting an argument. You will find abundant examples of this kind of reasoning from politicians, mass media and personal comments. Not recognizing and understanding this is a major reason why people reach conclusions which do not reflect reality.
Here are some notable examples I have run across:
Roseanne Barr: ‘Traitor’ Palin’s Followers Are ‘Dumbest People on Earth‘