Gender Terms

While reading this recent thread by skepchick, I was surprised by this remark of hers:

I auto-delete any comment that refers to human males as "men" and human females as "females"

I typically use gender terms like "male", "female", "man", and "woman" mostly interchangeably. Is there some major difference in connotation between the terms "woman" and "female" that I have been missing my entire life?

I am not arguing that she is wrong to be offended by these terms, but I would like to rectify my ignorance on this issue.

Thanks, SRSD! I just discovered this subreddit tonight, and I am really enjoying it.