The major downside to coffee is that - eventually - you
require it to function properly.
And when you try to quit, you get withdrawels (lethargy, headaches, etc.).
It is a definite "habit" (much like a minor addiction). Eventually, with continued use, your body will rebel against the stimulation.
Gotta go and make that cup of java now.
Actually, I am
allergic to coffee now (after years of abuse) and depend on tea for my caffeine fix (but still get really wired if I use coffee very occasionally - like today when I am exhausted but MUST work).
EDIT: It is a definite financial "cost" factor - especially if you buy it at a store. Just $1 a day habit (McDonalds/711 "crap" coffee) is $365 a year and specialty coffees $1000 a year.