I feel like a fraud if I consider them in the abstract, and the time I was invited into an intentionally created such space online, I panicked, and the space wound up causing me a lot of stress even after I left.
It took a bunch of shower-thinking to pin some more of it down. Yes, I'm genderqueer. I came with clit & tits as original equipment. In comments to someone's entry discussing agenderedness, someone had some excellent phrasing and thoughts about how one can be agendered as one's own gender identity, and not have any problems with one's body, but the general public may see one's body, and misgender one into a gender identity box that is comfortable for them to contemplate. Me, if you ask me to pick one for always and ever, I get cranky. If you ask me what my current gender status is at the *moment* with two to pick from, more-man or more-woman, I might well average mostly-woman. My ideal body does not involve the traditional sort of major genital renovation.
The particular space that I was invited in to had a policy that was friendly to transgendered women, as it was supposed to be broad and comfortable: if you identify as a woman, you're welcome. But it also had provisions for gender-checking prospective members: new members should have at least one member of the existing community vouching for your declared gender identity. That unnerved me.
I traced it back to the assumption of a stable gender identity. I'm not uncommonly a woman, but sometimes I'm a man, and most often I'm a geek, doing geek things, and when I'm not anything else, I'm a lunatic. I can *be* a woman while I'm in a women's space, but it's usually a conscious performance. It's not natural. (I tried to be a girl in 6th grade. That didn't go very well.) I feel like most women's spaces carry the expectation that people who use them should always be a woman, unless they explicitly say that female-bodied genderqueer people are welcomed, or that genderqueer people are welcomed. (I'm not gender-neutral.) I am not always a woman, and I feel dishonest claiming that I am in places that I respect where it matters, or letting it be inferred from my presence there.
I have not felt the same level of Wrong from various women-in-technology groups. Those groups tend to serve two interrelated purposes: 1: to serve as a public promotional face for the awesome work that women and people who are publicly perceived as women are doing in fields where they are under-represented; 2: to serve as a place of refuge where those same women-etc. can get away from some of the day-to-day bullshit that they get because they are perceived as women in a mostly-male field. The feeling of "You get labeled as a woman, you may come hide here from all the bullshit; we have common cause as we are lumped together" is very different to me from the feeling of "We are all women here; we have gatekeepers to make sure that no-one who is not a woman manages to infiltrate our numbers". It also helps that my primary identified gender is geek, and those are geek spaces at the 0th level, while being women's spaces first.
Talking it out helps. Being able to say "I am genderqueer, so these safe spaces are not always appropriate for me", and having people get what I mean, helps. Having safe spaces that say "If other people perceive you as a woman and you need a place where you can get away from the bullshit associated with being forced into a woman's shoes", perhaps even better.
And now I'm thinking about other gendered safe spaces based on area of interest at the 0th level. There probably should be safe spaces for fiber artists and nurses who are men, because they are the minority in fields where the assumption is that everyone's going to be a woman. Probably others, but those are the ones that spring to mind.