I've stayed away from this thread for spolier avoidance and haven't read back too far, so sorry if I'm re-stating things covered before.
Decomposition: Instead of decomposing more and more, the zombies at some point become "mummified". They get drier and stiffer, but they don't rot away completely.
That makes some sense. But, walking, pushing on doors, popping out and scaring people expends energy. Where does the zombie energy come from? Even if the body consuming itself releases some energy, it is a closed system and would have to run down sometime. Probably pretty quickly, since the zombie default mode seems to be "shamble about."
Do we know that everyone who dies automatically becomes a zombie or does one have to be directly infected by one first?
No, the show hasn't actually stated that, but, many believe that's what the CDC guy whispered into Rick's ear. And truly, the plague had to start somewhere, so it makes sense that it started from people who died of natural causes (Or at elast non-biting causes) and came back and started biting people.
Yet we've seen bodies pretty well decomposed with no signs of life, like the one Carl took the bag of knives from.
My take on Herschel: He represents the "old world," which is gone, and not being able to let go of that has unhinged his mind. Whether the plague can be cured is one thing, but even a country vet should have enough scientific training to know you can't "restore" decomposed tissue. Crude as it was, Shane's meltdown should snap everyone out of following Herschel, and I expect he will be marginalized.
On Shane: I can't stand Bernthal's acting, but things did come together for the character at the end. He represents the id-driven, survive-at-all-costs "primitive" man, though the performance has been so mumbly and aimless it was hard to tell before. He doesn't have the human qualities we normally want in a leader. Rick does, and Rick showed he has a strength that Shane doesn't have in the final scene. But the question will be, does that even matter anymore? Is Rick's more "civilized" leadership still valid, or is it time for strongest to take charge and the weak to do what they're told? Ralph or Jack?
Justin