Half and Half
When you see a glass filled halfway up its height with water, do you see it as half empty or half full?
Wait. Stop.
Before you go any further into some kind of navel-gazing philosophical attitude answer about how you're oh-so-optimistic and blahblahblah, that's not what I mean to ask. I mean to ask it literally: do you see a glass of water that's actually half empty or half full? (And don't cop out and say "both", you sit-on-the-fencer.)
Me, I see it as half full. (By the way, I'm normally a little pessimistic.) And it's because I think about how much water I would normally get if I were to pour myself a "full glass". I usually leave myself some "spill margin" (that little space) at the top; sometimes half an inch, sometimes an inch, depending, but typically less than the thickness of the glass' base. So a glass that's got drinky drink in it halfway up its full height usually means it's got more liquid than half the "full" amount I would pour.
And thus, my final answer is "(more than) half full". It also explains why I snicker to myself pettily when I ask for half a glass of something, and they pour exactly that, giving me that bonus bit, unbeknownst to them. (Score that extra drop.)