I love being a female developer. When I go to a hacker night, I feel like Scarlet in GI Joe, Firestar with Spiderman and his friends. Sysadmins and DBAs are happy to answer questions for a smile. In interviews and in conference speaker selection, I stand out. Colleagues open doors and invite me to happy hour. Teammates respect me and enjoy my company. My gender is an asset in my programming career.
Yet - when I meet another developer, I don't expect to be taken seriously.
It's a subtle effect. It took me a decade to notice, but much less time to cope with it. When I start on a team, half of what I say is a joke. That way it's okay when my words are laughed off. I demonstrate competence with good questions - these are more welcome than statements. When necessary, I can be very assertive, forceful enough that the men in the conference room can't blow me off. These strategies get me past the initial impressions, and within a few days I have the team's full respect. Gender is a consideration only before they know me.
The effect is so subtle I can't call it a prejudice. It's a shortcut our brains take: categorization. I do it myself. In my experience, women tend to contribute less in discussions. They don't fit the image of "strong developer" in my head. This adds up to lower expectations than for a man, at least for a short time.
The scary part is that expectations influence behavior. Subconsciously we conform to the expectations of those around us. Because females are expected to be quiet, because they are interrupted more than men, women volunteer less. Which leads our subconscious minds to expect female developers to be quiet and contribute less.
The spiral of lower expectations can be reversed. For every woman technical speaker we hear at a conference, we'll take the next female developer we meet a little more seriously. For each woman who shows up to the user group, we'll be more likely to invite our female colleagues. Every time we direct a question to one of the women in the meeting, or ask an interrupting colleague to let the woman finish speaking, she's inspired to speak up more.
We turn this spiral around one tiny action at a time. Women, go to user groups. Men and women, recognize the bias and fight it - expect more from the women around you. Every woman can fly like Firestar.