Survey says that 51% of homosexuals are not out at work, and I don't blame them. It's one thing to be out and proud in public; it's quite another to wave that great big rainbow flag in the office where your boss passes out paychecks.
I personally have never been "out" at work. I've worked with people who knew I was gay, and they were always okay with it, but having friends know isn't the same thing. I'd be very afraid of someone who didn't approve of my life, especially a superior, and treating me differently because of it, whether that involves ignoring me, punishing me, or working me more or less because of it.
In fact, I've even lied about my orientation. Not so much ever to the point where I've specifically stated that I'm straight, but more so to agree with coworkers' statements. Most of them will talk about girls they want to get with or think are hot, and I'll very nonchalantly agree with them, quickly trying to change the subject. About 47% of LGBT people are supposedly guilty of this, according to that same survey.
It's going to be difficult getting people to feel comfortable coming out at work. Having an anti-discrimination clause for sexual orientation/gender identity/anything LGBT is one thing; getting people to be okay with it is quite another. I hope one day I'm comfortable being out at work.