A recent academic study found that while a number of sex-specific stylistic trends exist across the way people write on Twitter, these patterns aren't true for everyone.
The study concluded that a number of female users and male users do employ language more typical of the "opposite sex," and that a user's tweets are more likely to sound like his/her sex if he/she has significantly more Twitter friends of the same sex. (Know your audience, etc.) The researchers note that other factors like age, race, and class factor into the way people tweet, and they take a refreshingly non-gender essentialist stance: Men and women, on the whole, might tweet in different ways, but that's hardly nature's doing. Instead, this is a study about how we're learning to communicate with and from each other, which is fascinating.