Just finished an online quiz for the National Strength Association, NSCA, and as always I am very impressed.
Yes, caffeine is one of the most highly used substances in the world.  It's accepted in both the general population, and (maybe to your surprise), the athletic community.  Bear in mind, some athletics consider it illegal at a certain urine concentration.  

Caffeine improves alertness,improves mood and decreases pain from it's indirect stimulation on the nervous system.  But did you know caffeine has been linked to  increase endurance, power and speed?  It's no wonder the National Collegiate Athletic Association (NCAA) and International Olympic Committee (IOC) monitor concentration levels in athletes. 

Caffeine stimulates mobilization of free fatty acids,  which could in turn help you perform endurance activities for longer durations at a given intensity.  Some studies have reported increase in oxygen consumption, improvement times, and improved skeletal muscle contractility.   Running anyone?  I did just recently read people who consume hot beverages (coffee) throughout the day are more likely to be in a better mood... 

But be careful, fast heart rate, anxiety, and insomnia are just some of the effects too much caffeine can have.  As with anything good-moderation is best.

Reference
1. Smith, T. MA, CSCS, *D, NSCA-CPT,*D.  Aerobic Benefits of Caffeine Supplementation.  Available at www.nsca-cc.org />