During Ubuntu Open Week, Mark Shuttleworth, founder (and funder) and leader of the project, made some statements that could be charitably described as "unfortunate":
(12:31:38 PM) sabdfl: not especially, but it makes the project more interesting
This bit had steam coming out of my ears. There was an unfortunate followup that the questioner has apologized for; you can see the snippet at Geek Feminism or the whole log. I should also mention that I've had the luxury of several days to chew on this vs. Mark's thirty seconds or so, and he apparently does poorly with public speaking. Having given equal time to Not the Point, I proceed to The Point.
(Ubuntu Bug 1: "Microsoft has a majority market share")
Diversity is absolutely fundamental to fixing bug 1.Mackenzie Morgan points out one reason: "since women are 51% of the population, if all women used Windows, it would be impossible for Microsoft to have a minority marketshare." I think this extrapolates pretty nicely to the contributor pool. Do we really have too many open source contributors (developers, writers, community managers)? Lack of diversity implies that we're not drawing from across the whole population, seriously hamstringing the effort.
The second reason is a spin on the first. Beth Lynn Eicher had a wonderful comment in her Resolving Bug One talk...which started an hour later. Intended as such or not, it's a brilliant response:
(02:41:34 PM) bethlynn1: and what you already have in common
(02:41:47 PM) bethlynn1: if there are people who look like you
(02:41:50 PM) bethlynn1: and talk like you
(02:41:56 PM) bethlynn1: who are using a product
(02:42:07 PM) bethlynn1: it gives a great deal of ligitamacy
(02:42:23 PM) bethlynn1: this is why it is important for diversity
(02:42:49 PM) bethlynn1: I spend the majority of my time when I give a computer away to women
(02:42:55 PM) bethlynn1: because I am a woman
(02:43:36 PM) bethlynn1: I do tell men about how great Linux and free software is too
(02:44:20 PM) bethlynn1: but it is easier for me to speak the language for a woman to another woman
She takes a commonality of background and leverages it to bring someone into a new community, a sort of anti-Othering jujitsu. It's the flipside of the psychology in play with e.g. sexualized environments, used to unite instead of divide. This idea extends beyond outreach into development: you get a product with a broader appeal if people with a broader range of backgrounds work on it. More perspectives brought to bear.
I lied...Shuttleworth had more than thirty seconds to think on the topic. He had over a month. Frustrating: here's a guy who's literally spending his life and fortune on bringing computing to the less fortunate, particularly the developing world--it comes through in almost everything I've read by him--but that commitment doesn't seem to extend to diversity in the project itself, or a realization that diversity can help achieve his goals. Fortunately, plenty of people within the project do Get It (including his CTO). But Mark...the more women involved in developing Ubuntu, the less trouble you'll have "explaining to girls."