Spirit had been communicating on a once-per-week schedule in recent weeks. During the designated time for the rover to communicate with NASA's Mars Odyssey orbiter passing overhead on March 30, Odyssey heard nothing from the rover.
Just a little update here to post a Navcam panorama from Opportunity showing that the rover successfully arrived yesterday at the doublet crater she's been aiming for since she left Concepcion a couple of weeks ago.
I saw this image at the Lunar and Planetary Science Conference so am happy they released it: a view of Opportunity sitting on the north rim of the little, fresh Concepción crater, taken on sol 2153 (February 13, 2010).
I wrote earlier about some results from Spirit reported at this year's Lunar and Planetary Science Conference in Houston, Texas; here are the rest of my notes on rover-related talks, from Opportunity's site on the opposite side of Mars.
I think a goodly proportion of you readers have already figured this out for yourselves since it was launched last March, but I didn't download and install it until last weekend, so this is new to me: Google Mars is awesome.