Fodder for both sides of the cell phone debate
A Harvard study shows that cell phone usage in cars does cause an increased number of accidents, but that the economic benefits of cell phone usage is comparable to this cost. (This article is frustratingly vague about whether the benefits refers to the benefits of all cell phone usage, or just the benefits of using your cell phone in the car, which is a rather important difference.)
While my attitude towards cell phones has mellowed considerably over the past few years, I still have no patience for people who act like idiots on the road, for whatever reason (save your snide remarks, you), and so I do reflexively feel annoyed when I see people talking on their cell phones, probably out of the fact that this may cause them to do something stupid.
The thing I fear the most are the cell-phone defenders pointing to this and saying that it's still worth it on a utilitarian basis. I have one word to answer that: externalities. If you plow into me because you're blathering on your phone, I certainly don't reap any of the benefits of your usage.