I've been reading Born to Run (see what you mean about the writing style Greenlegs!) and it's pinned down for me what changed in my mindset when I nailed W5R3; running shifted for me to something I can do with pleasure again, I find myself looking forward to the next run and scheming to make sure it will fit in with anything else I have planned.
A couple of other things I've picked up are the importance of an economical running technique that minimises stress on the body (shufflers rule!) and the comment about the running speed of the "persistence hunt", about 10 minute mile pace on average.
The section on running and evolution is absolutely fascinating.
I've been googling the ultrarunners mentioned with increasing astonishment too!