The word came from Square Enix's Lodestone site over the weekend, announcing that the servers would be shut down due to Japanese power companies requesting energy conservation. It's currently planned for a week, starting from yesterday. Square's PlayOnline servers are also unavailable, including the Friends List, password recovery, and account cancellation.
The pair of natural disasters have impacted power production from nuclear plants, leaving large areas of Japan without power. If you'd like to contribute more directly to aid in Japan, you can donate to the Japanese Red Cross Society.