re: is opportunity in a crater
Looks that way, doesn't it.
[Initial analysis of the images suggested Opportunity landed within a shallow crater. Its low rim shouldn't block the rolling robot's path once it gets going, Squyres said.
"It's smooth sailing to the horizon," he said]
sfgate.com
From where Opportunity rests and the horizon line, here's a definite concave look to this new area that wasn't there with Spirit's landing site. Must wait for more news.
From looking at the image of Opportunity's landing site posted on the 24th, at (verrry slow site right now!), there are several shallow craters in the area.