Jan1305: Some of the answers here are very curious, considering the anti comments usually made about first night sex.
Why aren´t people consistent?
Personally, I don´t think there can be rules, we are all different, however I would be more than a little worried if three months down the line, nothing had happened!
It's because those posting that here aren't the ones who say that they wouldn't have sex on the first date.

I, for one, remain consistent with saying that I've done it, and that it's whenever it feels right. I have learned not to have the 3-drink rule anymore, though.

I've been smart enough to learn from my past and get to know a person a little bit better than that.
But, if it's someone that I have known either by online and phone for a while before meeting, or in person before we go on a first date, then I wouldn't say no on the first date if the feelings were mutual. I go with the flow in life, and hold no regrets for that. If it doesn't feel right to both of us on the first date, then it waits until it feels right.
And no, I'm not saying you were pointing a finger. Just explaining why some might seem inconsistent at times from my own experiences and posts on the subject.