Additionally, as SimsVIP reports, you can spot a Playfish SimCity Social URL ... if you load up http://apps.facebook.com/simcitysocial/ in Google Cache, stop the page before it redirects to Facebook, and view source. It's a lot of crazy steps to take in order to see some shaky, uncertain evidence, but it works.
Even if this game turns out to be real, there's no telling when EA will launch it. Outernauts will likely be EA's big Facebook launch this summer, and the publisher has been sitting on these URLs for months. Perhaps it'll be released next year alongside the other new SimCity.
Update: We came across this URL for a currently inactive "SimCity" app. The source, including the broken image on the front page, links back to Playfish. EA officially declined to comment to Joystiq.