For me, I thought we would find out a lot more about Lily and James' past, because I thought that the way they "thrice defied" LV was going to be very important. I thought this would have explained why LV assumed that the prophecy referred to the Potters rather than the Longbottoms, who were very popular in their day. Neither of these concepts are particularily clear to me.

This indicates to me that precious few wizards - who have explored the limits of magic to an extent far beyond the norm - even know if its existence. DD and LV certainly fall into this category; I get the impression that no two wizards have ever delved that deeply into magical understanding before.

This begs the question: how can such a blind point of view exist in a human being? Isn't the ability to understand love like this the very thing that sets us humans apart mechanical life forms, or even from the rest of the animal kingdom for that matter?

"You've got to really feel what you've done… Apparently the pain of it can destroy you. I can't see Voldemort attempting it somehow, can you?"

Lirene. From what I have read, all I can gather is that they didn't know of it until Harry said something so they could make the connection.
Dumbledore is very good at assumptions, but turning assumptions into facts is another matter, which Dumbledore is also very good at.
Dumbledore knew the Avada Kedavra curse didn't work, he knew the curse rebounded, and he knew the curse left a scar. Therefore he knew something ELSE was at work that evening.
Voldemort never realised that Lily's Love was what kept Harry alive, primarily because Voldemort has never tried to understand Love. He certainly got pieces of the puzzle, but never the entire puzzle.
Voldemort only realised what had happened once Harry had told him what happened, but he never saw it for what it truly was.

How did they know so much; meaning, how is it these two wizards delved so deeply in magic. Because at least to me, one has to want to read or learn about magical sacrificial protection. Could this information be found in "Secrets of the Darkest Arts"? Or is it they knew so much that they could put two and two together? That the "old magic" Voldemort was referring to in the graveyard in GOF meant that he understood "blood" as in related to; the old magic of families?

I will attempt to answer your question harrypottergeek2. I believe that with the creation of each and every one of Voldemort's Horcruxes, he became less and less of a man; less human. He could no longer have the same feelings as humans do simply because he didn't want those feelings; each time he murdered someone, he tore his soul. It has been argued that every time Voldemort tore his soul he did so in equal parts. I tend to disagree with this. I think it would be impossible to choose which part of your soul you don't want. So, with each and every bit that is torn off, he loses whatever emotional capacity that soul bit had to begin with. This is also the reason why I don't think Voldemort could have repented. Even if he wanted to, I believe he did not have that part of his soul anymore; the will to repent was torn away from him. Does anyone believe that Voldemort truly had the capacity to repent? Because even Hermione has doubts in DH:

Here's another question (am I allowed more than one??). In the forest, when Voldemort hits Harry with the AK, both fall unconscious. Does anyone think that Voldemort got a glimpse of what his soul eventually became? Was he able to see his mutilated soul and comprehend what it was? Or was he too blind by his own power to even notice?

Love like this is not strictly a human emotion, it is what helps a mother nurture her children in the wild until they are old enough to fend for themselves. Mating is generally for the continuence of the species. It is certainly what sets Flesh & Blood apart from Mechanical objects.
Remember, the needs and wants of non-human creatures are not the same as ours, therefore their needs and wants may be something we don't fully understand.

Well, we all know that LV wanted to split his soul into seven pieces. As far as most are concerned he did this. 6 material Horcruxes and the final being the soul left in his body. Of course he didn't know that Harry was a horcrux. What if there had been a 7th material horcrux he made? What if he didn't consider the soul in his body to be the 7th? There could have been 7 material Horcruxes, not counting the accidental Harry Horcrux and the soul left in his body. If there was one left that no one knew of or ever found he could still be out there somewhere. Perhaps, 19 years later he is still in a weakened state somewhere trying to regain his strength. Maybe, the next generation of Hogwart's students and a new order will still have to deal with Voldemort. It is possible that he could be somewhere trying to recruit one that will bring him back to power. MorseMordre!