attraction is 50/50 down the line, or is it more like 60/40 or 75/25?
What is "attraction"? To me, attraction - TRUE attraction - is something that is completely unbiased - that moment when my heart skips a beat, or my brain seems frozen. Two days ago, I had three breath-taken moments after making eye contact with three new people I had never seen before. Two of them were men, one was a woman. This is pretty typical for me, so instead of a percentage, I will give you a 2:1 ratio.
varied over time since you were in school? and does it vary slightly depending on the season, or perhaps on your mood?
Hehe this is funny. Good question, though. My attraction has never varied. Honesty about my attraction has changed, however. At this point, I am completely open.
The only "pattern" I can recognize is my occasional tendency to desire the sex opposite of whatever I was most recently involved with.
Has your attraction to either gender ever wavered or disappeared?
Just when it does, some fateful event will re-enlighten me to the losing gender in a whole new, exciting way.
Do you watch as much straight porn as you do gay porn?
Definitely not. More gay porn, for sure.
Do you find a difference between what you are sexually attracted to vs what you are emotionally attracted to, in other words, are you more likely to have sex with one gender but more likely to fall in love with the other?
Great question... I'm more emotionally attracted to men, and can learn to love their bodies more easily than I can a woman's. Women are fascinating to share emotions with, but I don't usually want to have sex with a particular lady more than once. Unless it's been a while
Did you always realise you were bisexual, or did you once think you were either gay or straight? Do you find people's reactions to be negative, even more so than if you were gay?
I've ALWAYS known I am bisexual. Period. But that's different from what other people think I've known. I've come out of the closet, gone back in, come out again, bla bla bla. Different groups of people - depending on: how judgmental they are, how socially comfy I am around them, where I'm at in terms of development at the time I've known them - all have heard me represent different sexualities. I've learned that people are quite a bit more comfortable when you identify yourself as STRAIGHT or GAY. Some people are quite negative about my being bi, yes, but I think it is only either out of jealousy/pride.
Was there more pressure on you from your community/religion/family/society to deny your homosexual side because you already found women attractive?
Actually yes. When I came out as gay in high school, my mom wasn't upset or disappointed, but simply did not believe me. And tried to talk me out of it! According to her, she'd never observed any behavior which would suggest my being interested in men. Oh, if only she knew. My parents would never hold my sexuality against me, however. So I lucked out.
Is it more common or less common for bisexuals to be 'out' to everyone?
I really don't know. I think it depends on the bisexual. Some people don't have to be out. Some people don't ever have to mention that they're out. Some people just do whatever they want, and others may think they're gay, some may think they're straight.
It's when everybody KNOWS me as one or the other, then something I do contradicts that (I dated a girl - peers saw that - then they saw me with a guy, and are completely lost), that folks get curious and confused.
Is bisexuality more common in women than in men? Is it perhaps easier for women to admit to than men? If so, do you think that far more straight men are bisexual than they let on?
I certainly hope it's not more common in one sex than the other. I don't think it is. I believe we are all inherently bisexual, and perhaps hormones decide what our dominant sexuality will ultimately be. I think one's hormone levels are influenced by equal parts genetics and environment. But I dunno

Maybe that's just my particular case! I don't speak for everybody.
You ask a lot of good questions, it's great to see people approaching the subject with such thoughtful curiosity. Cheers, partner.