Sadly, most of what can be said at this point would be speculation. I personally don't find them that scary, but that's because of what is known. Basically, invert your natural instincts. Charge at an Endermen if you do happen to look at one (because they freeze and don't do anything), and bash your sword into them. Unless Endermen have a "Zombie Pigmen" like property you'll never lose if you do this.

This video was confirmed fake, but it gives a good idea of what kind of threat Endermen are from what is known so far. Honestly, you're an idiot if you did this:
http://www.youtube.com/watch?v=DIeQgwEJUms

As for blocks, I don't know what to say. It's no issue if they can only pick up dirt, gravel, or sand; but I guarantee you there'll be a huge outcry from many people if they can pick up any (or almost any) block.

From what I understand, the Endermen are a play on the concept of Slenderman.  If you don't know what that is, check out MarbleHornets on Youtube.  With that concept in mind, you have every reason to be freaked out by these things.  :C

Yeah, I saw the Slendermen thing on the Minecraft wiki. That's also when I thought of what kind of psychological effects it might have on some people, considering the fact that Slendermen is used in some creepypasta's. But as always, you'll have some people who think it isn't scary at all, and think that they're too easy to deal with. For instance, me and Miles

Finally a new mob, I have a reason to go back to Minecraft now, Endermen are hopefully as scary as Notch made them out to be so there is a constant fear in the game, almost like there was when I thought HeroBrine was a mob.

Him using the term "nerf" could mean just about anything...

1.) He omits it entirely, though I think he probably would have just said it if that were the case.

2.) They only pick up blocks under certain conditions  (yeah, okay, i dunno what those'd be so...)

3.) They drop the block they are holding upon death.

So anyway, yeah.  We'll see where that goes.