Rob's point in the other thread that there are three billion women and so three billion answers to these questions is a good one. I would only temper this with the observation that a large percentage of people, men and women, don't know what their sexual preferences and priorities are.
Experience counts for a lot, if you allow yourself to have it. I think a lot of the disparate points here add up to the issue.
We are bombarded with expectations, either of the Jessica Simpson type (I'd never heard of her btw till she was mentioned here) or some hot hung eye candy on the other side. So I can't blame LemacST for his insecurity/inquisitiveness, but it is the wrong question. Is my penis big enough? I don't know, go and have sex with it and find out, I'm sure it is. But don't imagine that you will leave three billion women in a post orgasmic haze.
What happens though as you gain experience, is that you learn what you both like and need in terms of priorities. If you were lucky enough to know these when you committed to a partner and shared them, then, as Big Dreamer is saying, you are likely to have a good ongoing relationship. Though of course people's priorities change and sadly once shared priorities diverge.
Getting back to size specifically, I wonder if my experience is common? I had two longer term relationships in my late teens and twenties that ended because of incompatability. We could have sex, but it hurt me often, I ripped my frenulum on a regular basis and i think I ended up with something of a penetration phobia - anyway they both ended despite everyone telling us that we were the perfect couple blah blah blah and the lack of sexual satisfaction was clearly a part of that. This is why I am always interested in Love-it's perspective. Strangely now though, I do have one friend who I see on a regular basis with whom I can't have full sex, but we have great fun otherwise. The expectation desire for the perfect relationship union is not on the cards so we can just have fun anyway.
So, whereas you hear a lot of women say that size is more important for recreational sex than in a long term relationship, I would say the opposite for me.