|MadSci Network: General Biology|
According to the caffeine FAQ ( www.cs.uwaterloo.ca/~alopez-o/Coffee/caffaq.html) the lethal dose of caffeine is 10 grams, which translated into 50-200 cups of coffee, which would have to be consumed at one sitting. You would be throwing up from overindulging well before you could drink enough coffee to kill you.
Note, however, that the side effects of caffeine include nervousness and rambling thought and speech patterns. I therefore do not recommend pumping up on coffee as part of a regular study routine. It doesn't do you much good to be awake if you can't concentrate. If you enjoy coffee or other caffeinated beverages, enjoy them in moderation, but don't plan on using them to get you through regular all-nighters. Get some sleep and plan on studying during a time of day when you are alert and relaxed.
More information on caffeine can be found at http://en.wikipedia.org/wiki/Caffeine and http://www.vhs.com/literature/caffeine.html.
Try the links in the MadSci Library for more information on General Biology.