From the NY Times of 20 May 2010:
Meanwhile the Martian Rover Spirit may be fighting for its life. Since it could not relocate is solar cells, and since the winter solstice has just occurred, Spirit has not been heard since 22 March.
Lowest temperature for the Rovers is -40 degrees. Spirit was below that temperature when it shutdown. Hope is that Spirit has gone into low power mode - to put all its power into keeping warm. So NASA's deep space network has been listening. Hoping that Spirit will wake up and transmit. If it can generate enough power to turn on the transmitter. And if it survived temperatures below what it was designed to withstand.