That should influence you to take what they say with a grain of salt and verify the facts, that doesn't mean they are wrong.
Example:
grlfrnd: The Clinton administation could have prevented the 9-11 attacks by reacting more stongly to the terrorist attacks during his administration.Ad Hominem Attack: grlfrnd is a member of Free Republic which is just a bunch of Clinton haters, so Clinton couldn't have done anything to prevent the 9-11 attacks.
Does that mean that grlfrnd is wrong about Clinton? No, it may indicate you are biased one way or another, but it doesn't mean the actual statement you made is true one way or another.