Never drank coffee before in my life, have no plans to start.
First of all, I could never get into the taste of it. I'm guess my palate is unrefined, but I only tend to eat and drink things if I enjoy them the first time. Coffee tastes like chalk to me and that's enough reason to stay away.
Second, caffeine does not affect my concentration or cognition. At all. My dad can drink a Mountain Dew with dinner and have trouble sleeping. I can chug Red Bulls and go to sleep a half an hour later. So I never saw the need to "drink coffee to stay awke/or focus".
That said, it kinda sucks not to drink coffee since it's such a social beverage. I've noticed a lot of attendings like to use the "let's meet for coffee" or "Have a minute? Let's grab a coffee and talk" to get to know you better or discuss stuff. Of course, this doesn't preclude me from drinking something else, but I sometimes feel awkward grabbing a water, a soda, tea or hot chocolate.