I eat alone at lunch all the time. It’s good for thinking or getting work done. Until recently, though, I hadn’t eaten in a real restaurant (as opposed to fast food) for a long time. It was okay, though. I had a book.
I almost always eat alone (especially lately, since my friends have been too busy at work for the past four months to have any time for me). The only problem is that a lot of restaurant tables are too small for both book and plate.