Source: http://www.squidoo.com/myths-about-anacondas

Myth #1: Anacondas are Habitual Man-eaters
The perception that Anacondas are habituated man-eaters is wrong. They have been observed to attack humans only when attacked, startled or harmed. They prefer to retreat in face of confrontation and attack only as a last option of self-defense.

Myth #2: A Very Gigantic Snake
Although the anaconda snake is a gigantic creature, it is not as long as fifty feet neither does it weigh two hundred kilograms. The biggest of these serpents make it as far as thirty-five feet, and almost never weigh past one hundred and fifty kilos.