This is perhaps a good time for some introspection. At the LinuxChix BOF at Ottawa Linux Symposium, we finished listing all the reasons why women stayed away from LUGs. A man from the local LUG raised his hand and said that no one at his LUG did any of the things we complained about, but they were still having difficulty attracting women. A woman from the same LUG raised her hand and said, "Yes, they do." She went on to say that only a few "bad apples" were doing these things, but those few were enough to drive off most women. This is a very important point: if your group has nine helpful and polite members, and one rude, sexist, loud member, most women are going to continue to stay away because of that one member. I realize that this isn't fair to the other people in the group, but that's reality. If your group is stuck with one bad apple, try a little peer pressure the next time he does something that will drive off women. Reply to his email, disagree with what he says--establish that you don't share his opinions. Just knowing that there is one other person in the group who is willing to publicly disagree with the "bad apple" will help immensely, and will make women more willing to stay.
In my own experience, I have over and over again heard a man say that he doesn't do any of these things, and then observed him hours or minutes later doing exactly what he claimed he doesn't do. I don't think any of those men were lying, just completely unaware. Making sexist jokes or comments seems to be the most unconscious behavior - many men just don't realize that what they're saying is offensive to women.
Also, it's definitely possible to have good intentions and still drive away women. You may think you're encouraging a woman by congratulating her on being brave enough to show up to an event, but you're actually pointing out to her that she's weird and unusual, rather than making her feel like part of the community. As one woman put it, "I know I'm an alien. You don't need to emphasize it." We're hoping that this HOWTO will help you realize when you are unintentionally driving away women.
If you're curious about how your behavior appears to women, my best suggestion is to find a woman you know who tends to be blunt and outspoken, and ask her if she remembers you saying or doing something offensive to women. You might be surprised at her response. Remember, most women would rather chew off a leg than be rude to a man to his face, so it may be difficult to get an honest answer.