http://www.cracked.com/article_18704_5-mind-blowing-ways-your-memory-plays-tricks-you.html
Really interesting read - I would copy/paste the whole thing but there are a lot of pictures and a video.
A couple of things that stood out to me:
"We judge things to be true based on how often we hear them. We like familiarity, and repeating a lie often enough makes it familiar to us, the repetition making it fall right in with all of the things our memory tells us are true about the world. Every advertiser or propagandist knows this. Humans are social animals, and there is a primal part of us that still says, "If other members of the tribe who I feel close to believe this, there must be something to it ."
" The biases in your system cripple even your ability to examine your own biases. So just now, when you thought to yourself, "Ha, I've caught myself doing that! But at least I'm not as nutty as those 'Obama is a Muslim' nutjobs!", you just saw your own bias at work. You're trying to examine a broken mechanism with a broken mechanism. It's like trying to perform surgery on your own ass, with a scalpel that is itself clenched in your ass."
"...experiments show that if you run into someone who knew you as a child and they tell you about an event you don't personally remember, you'll construct a memory to match it--even if it didn't actually happen. It's like we have evolved to be able to lie, but still haven't gotten to the point where we can get our minds around the fact that other people do it. As with the first entry, we find our memories are putty in the hands of people who know how to manipulate them."
Basically, our brains all suck. 