I tend to eat "alone", but this is because I'm usually talking to the wife, taking a power nap, reading, or otherwise distracting myself from work. I typically have a lot of high pressure items on my plate and need the time for my brain to sort out and come up with solutions... and the main way is to distract my conscious mind and let my brain work uninterrupted. Yes, it's fun to take lunch with others, but often I just need a break from everyone and everything.