Newb questions... Be gentle.

[Shohan]

So I dropped my old school Droid and since I wasn't impressed with the Thunderbolt I upgraded to an iPhone 4. I've played with them before, but so far I'm pretty impressed. I've got some newbie questions. I did lots of searching, but wasn't able to come up with much in the way of concrete or understandable answers. 32GB iPhone 4 with 4.2.6 jailbroken with green pois0n RC6.1

What is an SHSH blob and why should I back it up? It's a unique hash for my device or something right? And pretty much so I can downgrade if I needed to?

Why are there so many VZW iPhone 4s on Ebay?

With the iPhone using iTunes does it report back to Apple if the phone is jailbroken or not? Using unofficial apps? (From Cydia for example.)

Someone had mentioned that green pois0n was detectable by Apple where redsn0w wasn't. Something to do with an iTunes authentication issue. Any info on this?