Who? Me? Psychologist James Pennebaker from the University of Texas at Austin discovered that "if people were asked to write about emotional upheavals, their physical health improved and the ways people used pronouns in their essays predicted whose health would improve the most. Specifically, those people who benefited the most from writing changed in their pronoun use from one essay to another. Pronouns were reflecting people’s abilities to change perspective."
If you think this trivial consider research that found that poets who committed suicide used more I-words than non-suicidal poets.
So does it matter if you're a man or woman? Yes. Interestingly, women use more I-words and cognitive words like "because" and "think", than men. There is actually no difference between the sexes when it comes to emotion words like "happy" or "sad".