I'm not an American, but like many people I'm aware of the Fifth Amendment and how it is often lampooned. I recently discussed this with someone, and I can't for the life of me remember who, was it Peter at BLUG? If it was you, you'll enjoy this.
The discussion centred about why it would be remotely helpful to plead the fifth since it seems to make it 100% clear that there is blame to be apportioned. Quite by coincidence this week I came across this Slashdot story about a man arrested for taking picture of an ATM. The comments discussed how it can be generally unwise to argue with armed law enforcement officers. I've frequently made similar points, and also about customs officials and giving them a legitimate reason to don surgical gloves.
Someone posted a link to this fascinating law lecture given by Professor James Duane who argues cogently that one should never talk to the police without protection, that it can never help you, but may harm you. A police officer is allowed to rebut and give the last say, and this is equally interesting. Definitely thought provoking.