I feel google is a value company. I rarely see companies block google in their intranet. Nowadays google becomes part of most of the people's daily life. As a developer i can't imagine how life would be without google.
But facebook is blocked in all the companies i worked for. Why? because that is a place for squandering, not for productivity. Companies may use facebook to market their products, but they don't want their employee access facebook. that is the irony.