A while ago on one of the Usenet groups I read, a person started posting regularly without specifying their gender. I barely noticed that they had never actually stated whether they were male or female, because to me it was just glaringly totally unavoidably obvious from their writing that they were male. Anyway, a bit later someone explicitly asked them whether they were male or female, and they refused to answer, and various other people started guessing. I was astounded at the number of people who thought the poster was female. In fact, I've just been and re-viewed the whole thread and the "female" guesses outweighed the "male" guesses by a significant factor.
Much later on, another post by the same poster made it obvious (given the previous context) that the poster was indeed male. Aside from thinking "hah, I was right" I didn't give it much else thought but it's been bubbling away in my brain for a while.
So, if anyone finds this topic interesting, leave an anonymous comment (either your own writing or someone else's) and I'll try and guess whether it was written by a male or a female author. Anyone else is welcome to add their guesses too, and I'd also be interested in any reasoning behind those guesses. The only rules are that the comment has to be long enough and relevant enough to give me a reasonable chance (posting a one-liner joke or an excerpt from your dishwasher instruction book does NOT count :-)). Something like "what I did at the weekend" or "what I did yesterday" would be ideal.
If you want you can (instead or as well) leave a comment where you try to write as the opposite gender.