A case study just out in CNS Spectrums describes an apparent case of ‘caffeine-induced psychosis’. The summary is below although the full paper is available online as a pdf.
If you’re a regular coffee drinker, I don’t think you should worry though. It’s impossible to say whether caffeine was the definite cause in this case, and the gentleman concerned was drinking about 36 cups of coffee a day.
Caffeine-induced psychosis
Hedges DW, Woon FL, Hoopes SP.
As a competitive adenosine antagonist, caffeine affects dopamine transmission and has been reported to worsen psychosis in people with schizophrenia and to cause psychosis in otherwise healthy people. We report of case of apparent chronic caffeine-induced psychosis characterized by delusions and paranoia in a 47-year-old man with high caffeine intake. The psychosis resolved within 7 weeks after lowering caffeine intake without use of antipsychotic medication. Clinicians might consider the possibility of caffeinism when evaluating chronic psychosis.
Mind Hacks 
Reminds me of this excellent song: http://www.youtube.com/watch?v=-UsR9Ap41R8