I voted for 300mg though I think that's an upper limit for me...on average I expect I'm around the 150 range, but on an average day, around 200-250. I frequently have a cup (12-16oz) in the morning, and I might have a tea or something later in the afternoon/evening. I grew up drinking tea several times a day (including at bedtime!) and it doesn't seem to affect me the way coffee does. On bad days (too little or bad quality sleep, snoozy weather, etc) I might have a second coffee in early afternoon (12-3) but if I make this a habit I have found I get twitchy, anxious, GI upset, and withdrawal headaches :/ Best way to avoid those symptoms, in my experience, is to (a) taper off and (b) have green tea! (I don't know why. Might be the small hit of caffeine plus good amount of water is good treatment for the withdrawal.)
As long as I stick to 1 coffee/day, though, I've been pretty okay. However, my bf has read and shared that our bodies get conditioned to caffeine and get lazy producing the neurotransmitters that wake us up ('cause they don't get used, 'cause we have caffeine in those spots!)...I may have felt this happening so I got myself some decaf for the mornings where I want the flavor of coffee but not necessarily the caffeine. But anxiety/headaches didn't contribute to that choice.