Most of the research on coffee that I've seen is mixed-to-modestly positive for moderate amounts (1-2 cups day). Essentially: if you're having a few cups, have no problems with it, and enjoy it, no need to stop. Some people do experience sleep and stress problems.
I've found that relying on tea through the course of the day (after a morning mug of espresso) keeps my energy levels more even. Dittos knocking off the carbs -- much more even energy levels, and no post-lunch slump.
