I've always been pretty open about who I am. On my OKC profile the first words are "I'm a FtM chap..." I figure if I'm up front about who I am, it'll save a lot of heartache later.
At least that was the plan. I was dating a gay man who said he was attracted to me, we had loads of sex, and just as we started getting attached to each other, he popped up and said that he was more attracted to cisgender men who have real flesh and blood penises. Because I don't have one, he decided there was no future with me. And even though he loves me, he can't have sex with me because he's getting really attached, blah blah.
So. Yeah. Even being open and honest about who you are will sometimes lead to bullsh*t.
However, I still recommend being open about it. Not only so you can weed out potential gits, but also because we need more visibility.