I get the same results; every email, blog post or short story I feed in there comes out as 'male' (or in a couple of cases 'Weak Male' whatever that's supposed to mean).
I think it's still largely based on stereotyping and cultural constructs of how women and men typically communicate, not yet another proof that males and females are oh so innately different. Then again, any tool, survey or study yielding the results that women/men responded stereotypically above chance elicit the belief that male/females are fundamentally different, even though a large number of people did not respond stereotypically (but are usually ignored or explained away). From the gender guessing program itself, I find several clarifications annoying:
The content, knowledge of the material, age of the author, nationality, experience, occupation, and education level can all impact writing styles.For example, a woman who has spent 20 years working in a male-dominated field may write like her co-workers. Similarly, professional female writers (and experienced hobbyists) frequently use male writing styles.Gender Guesser does not take any of these factors into account.
So a woman hanging out with and accepted by men ends up having writings that masquerade as a male's. It is not that females can innately write in any form, genre or style whatsoever based on their own interests and personality (or vice-versa for males). It's also not that it's silly to assign male/femaleness to genres and subjects in the first place beyond already-established stereotypes and tradition.
Also (emphasis added):
While Gender Guesser may be 60% - 70% accurate, it is not 100% accurate.This is better than random guessing (50%), but should not be interpreted as "fact". In particular, men should not be offended if it says you write like a girl.
In order to reassure the unfortunate men who may be compared to a 'girl', they basically admit that their doodad- and its results- is actually, probably flawed and will often guess wrong. Because who wants to turn out writing like a female, or (worse/better?) a Weak Male!
With this in mind, such efforts don't say anything about innate gender differences or writing but a lot about deeply ingrained, cultural and traditional stereotypes.