So FSP posted recently here and here about eating "al desco". She seemed to confuse the issue of eating at your desk with the idea of working through lunch.
Honestly, when I'm in the office, I almost always eat lunch at my desk. But it doesn't have anything to do with work - that's when I surf the internet. Hell, ever since I first got internet at home, I've eaten breakfast every morning in front of a computer. Yes, I do need to shake crumbs out of my keyboards on a regular basis.
I find it almost impossible to eat while doing real work in the office. Even if I'm on the phone, I'm shuffling papers, scanning documents, or taking notes. In the field, it's a little easier to grab a bite while you wait for readings to stabilize or for the driller to fix whatever just broke.