anecdotally, i always struggled focusing with caffeine. look into green tea; it's not only very healthy but it's more of a calm and alert type of focused, no jitters or bursts of energy. 3-5 cups seem to work best for me.
I've been caffeine free for over 7 months and the health improvements make a good sized list:
• Better digestion due to the lack of caffeine induced peristalsis
• Insomnia completely gone
• No feeling "hung over" every morning prior to consuming caffeine
• No swings in energy level during the day except those traceable to hunger or physical fatigue
• Complete disappearance of mood swings, both hypo-manic and depressive
• Increased productivity due to a better ability to focus for long periods of time
The one complaint that I have is that my creativity has dramatically decreased during this same period. Gone are the racing thoughts and flights of invention that had me continually coming up with new ideas. Still working on a controlled, non-chemical way of getting back to that creative state...
Of course, YMMV, but if you suffer from depression or any form of bipolar or seasonal affective disorder I highly recommend getting off of everybody's favorite drug. It may be affecting your life far more than you realize.
It seems like those that drink caffeine when they wake up or to wake up have the worst symptoms, especially when going without it.
So I don't think I was even actually consuming very much of the drug. Rather, I believe my body processes caffeine very slowly.
Also (from the wild intertubes):
amount of caffeine in an 8oz cup of various teas and coffee:
Coffee: 100 mg Black Tea: 40 to 50 mg Oolong Tea: 25 to 35 mg Green Tea: 20 to 30 mg Decaffeinated Black Tea: 4 mg Decaffeinated Green Tea: 4 mg