http://www.space.com/businesstechnology/070808_tw_rovers_update.html

To quote:

...the martian environment is actually pretty merciful during a major dust storm."

It turns out -- given all that dust flittering about in Mars' atmosphere -- the temperatures don't get nearly as cold at night. And that means that nighttime survival for a rover becomes much easier than it is when the skies are clear, Squyres advised. "So I think there's a good chance we're going to ride this out," he predicted.

Indeed, late last week, the news from Opportunity was good. Downlink data from the robot showed that the vehicle was in excellent health.

"The batteries are fully topped off, and the minimum nighttime temperatures have
still been within the acceptable range," Squyres reported. "In fact, we may decide soon to use some of that battery energy to conduct some science activities. This has a double benefit: It provides us with improved insight into what the weather is doing, and by running the computer inside the rover it also warms the vehicle."