I'm not a statistics major, so I was curious to know what Covariance does.

I highlighted two columns of data (processing time and input file size) and tried to run 'covariance'.  It popped up a dialog box, and the first clue something was wrong was that the three radio buttons are all checked.  Then when I hit 'OK', gnumeric must have gone into an infinite loop, because the entire system slowed right down, system load jumped to 7.0, switching to a terminal window and killing Gnumeric was almost impossible.

In short, there should be an error message along the lines of "don't do that".

Some might argue that people who know what they're doing don't need this kind of hand-holding, but I'd argue that it would be in Gnumeric's best interest to increase their potential audience, and even steal a page from Apple's and Microsoft's playbooks by making Gnumeric extremely education-friendly.  Make it an option, so it doesn't get in the way if you don't need it.