In the early days of my work life I started drinking a cup of coffee here and there. It helps if you're tired in the afternoon, and I like the taste. Then I started having a cup after lunch since everyone else went for it. Not long after, I'd have a cup first thing in the morning, and not too long after that I would be a complete zombie without drinking coffee from the morning and into the afternoon.
It took hard work kicking that habit, but I did, only because: (1) I don't like having such a strong dependency, it just seems unhealthy, and (2) I become irritable and jumpy in the evening if I have had coffee during the day. Maybe I'm just more sensitive, I don't know.
It sucks because I love the taste of coffee. These days I have a big jar of Nestle Instant Decaf at my desk and I dip into that every other day, just because I miss the taste of coffee, for which the instant just barely qualifies, but those are the lengths I go to. Now, if someone would come up with a decent instant decaf I would happily throw my money at that.