I can say for the girls out there: I do not mind pre-transitioned transgirls. At all. I've met a few, and no matter how "boy" they looked, I could NEVER see them as boys. One girl still had short hair so she could pass as a boy at school. But when I met her, she was in a dress. Even though she had big arms and was much taller than me, I didn't care. I saw beauty in her. For some reason, I just don't know what it is, whether or not a transgirl passes seems very irrelevant in my mind. I have met one who passed very well... she looked like a 15 year old girl. I was just like, "She a she? She's got to be." In the beginning when I first met trans people in person, I was very curious what they identified as. One transgirl I know looks totally guy-ish. Short hair, wears boys clothes. I called her a "he" once and felt really stupid. Then again, I wasn't sure because she is in the beginning of things still figuring things out... Now that I know, I can just totally not see her as a guy no matter how much she looks that way. I think she hasn't femmed up because her parents might not know...
It never crosses my mind that a transgendered person has me fooled. If they completely pass, I just think to myself, "Wow, they're totally themselves from the inside out. That's amazing."