I don't have the source handy, I think it was the "user's guide to the brain" or perhaps "accelerated learning for the 20th century" but caffeine (and other central nervous stimulants like ephedrine and cocaine) have been shown to improve memory recall. Subjects scored better on tests requiring remembering of facts after injecting caffeine.
It has something to do with the increase in beta wave brain frequencies. On the flip side the increase in beta wave frequencies make it harder to store new memories or think creatively.
I must have been in the learning book. I’ll take a look when I get home tonight. The point that I got from this was if I was trying to retain information it was better to stay away from stimulants and just relax and learn. If I needed to recall a bunch of information, say if I was going to be on Jeopardy, then I’d drink a nice espresso.
There was an article I came across that said not only does coffee appear to be very beneficial to the brain's memory function, but that they even believed it might be a weapon in fighting off early onset of Alzheimers. I will try to find the article.