I love coffee, and always wanted to be one of those people who can drink it all day. But I can only have one cup in the morning or early afternoon, or else I'm counting sheep all night.
I used to be jealous of people who can drink it like water, but now I appreciate my caffeine sensitivity. I had to pull an all-nighter recently to finish a translation job (remind me not to accept jobs that are mainly French legalese! English legalese is bad enough), and this time, I didn't want to crash the next morning. So I just drank a few cups of java and was able to stay awake until bedtime. Ta-da!
It still took me a few days to recover. My tendency to procrastinate is as bad as it was in college, but my ability to recover from an all-nighter sure isn't.