Yes, and that's a conservative lower bound (their web application servers likely draw much less than a kilowatt each and constitute a healthy portion of the fleet).

Global warming wise, should society really be focusing on using paper straws or should Facebook aim to make their server code 10% more efficient?

The good news is that electricity still costs a lot, even at scale, so there is lots of financial incentive for hyperscalars to make their datacenters and computation maximally efficient. To wit: there are a lot of people at Facebook (and Google, and Amazon, and Microsoft, and Baidu....) who work on making their server code more efficient. Small changes can result in millions of dollars a year in savings (in electricity cost, infrastructure cost, and opportunity cost in not needing to procure more servers).