After someone observed that a local developer conference had 48 speakers but none of them were women, many discussions took place regarding minorities, primarily women, at tech events. In this particular case it was a two day developer conference, but I've noticed it holds for smaller things like monthly interest/user group meetups.
The only real solution I've noticed, and please correct me if I'm wrong, is to aggressively recruit minorities. It was really late in the game, but one person did manually contact 60 women to see if any would be interested in speaking at this particular conference, but not a single one even responded to the email, let alone offered to come and speak. Perhaps the results would be different had that happened further in advance, but we don't know. I don't disagree that manually trying to recruit underrepresented groups is a good thing, but what else can be done? And what's making those people decide not to attend and/or not speak?
It's worth noting that this conference has a large percentage of attendees who are women. Women just aren't represented in the speaker list. Over the 4 years that it's happened, there have been a handful of women speakers. This may hold true for other events.
In an effort to better understand why people feel uncomfortable attending or speaking at events, I've put together a little survey. Every field on the form (except the last one to try to fool bots) is optional. If you enter your email, it will only be used for follow-up questions.
Here is a list of posts I've seen covering the conference that prompted all of the local discussion: