I've seen several posts discussing coming out as a way to be more honest about ourselves and to be who we really are as unapologetically as possible. I appreciate the importance of these things. However, I'm still not out to anyone I see on a regular basis except my wife. There are several reasons for that, and perhaps the most weighty in my mind is the fact that once out you can't go back in. The finality of coming out (whether perceived or actual) demands some pretty careful consideration.
As far as sexuality goes, I don't consider my attractions to be a "defining" part of who I am. They're significant and influence (probably) every aspect of my personality, but the sexual aspects themselves are purely private. They don't dictate my interests or behaviors and I consider them completely irrelevant in 99.9% of my daily interactions. So, in some ways, I just don't think coming out has much importance for me.
Some people have a much different experience than that, however, and would like to be open about sexuality and homosexual issues in their discussions and interactions with other people. I've felt this way myself, but when the issue is a discussion of my own sexuality (and not sexuality in general), I sometimes have to stop and really examine whether it's even appropriate to discuss my personal sexuality with whoever it is I'm chatting with. Sure, they're a friend who cares about me and loves me, but it's still a sacred and private topic. I'm not shy at all about talking about homosexuality or having explicitly sexual conversations in an impersonal, objective sense, but I tend to shut up (despite my occasional desire to "share" myself with friends) if I'm rational about it.
Perhaps the main reason I can think of for caution in coming out is that not being out has kept me away from temptation on many occasions. I have been to SO many professional meetings where I'm in a hotel far away from home and there is an organized group of GLBT medical students and physicians who, well, would likely provide plenty of opportunities to get into some hot trouble. I've been to their meetings to be supportive, but when I'm there I don't label myself as gay. I label myself as married with children and heterosexually active (or I would, if someone really pressed me for a label!). I read Abelard's description of a temptation with a coworker who was gay (and offered a sexual encounter!), and I suspect such a situation would have been exponentially worse if Abelard had been out to that coworker. I remember Max's description of a coworker who became obnoxiously determined to get it on after he learned that Max was gay. I've chatted with other bloggers who have gotten into trouble by "outing" themselves to others as well (once, for example, resulting in excommunication). Basically, I have plenty of temptation in my life without adding more. I'm pretty sure that I owe my 'gay virginity' to the fact that I haven't been out and have therefore had fewer opportunities to get into trouble.
I do see the benefits of being honest with close friends and loved ones about central issues such as this, and I am still considering whether, how, and when to come out to my parents. I'll do so when I see some real opportunity for benefit, and until then I plan to keep the private aspects of my life private.