Yea - we don't just need it for bitcoin either, we need it for all the social networks and centralised data-silos.
As to impossibility - probably no more so than bit-torrent before it was invented, and as far as I can gather, Bitcoin itself is exactly what you described - only it only records transactions. There may be a way of making a parallel model that stores sha hashes for "verified" data. Dunno - I'm a programmer, but I'd have to go into deep-trance mode for about a week to even start figuring this one out.
With regards transactions (rather than reputation management... oh, and an auction system and affiliate stuff etc)... with regards transactions, then what it probably requires is an API onto a bitcoin daemon - so people with genuine UX talent can turn the client into something that's not going to frighten away everyone who likes reassuring iPhone interfaces. This might already exist... I don't know, but the Pirate Party Founder guy was going on about this as one of the key-requirements etc, so I'm guessing it doesn't.
nope, you'll have to look for that one yourself. There are moves afoot to decentralise DNS though - and I think maybe Diaspora or Friendika are having a crack at it.
We're at war basically - and the attacks on wikileaks highlighted major weaknesses in the system... a decentralised currency is just a part of it. We need to decentralise everything... and the "troubles" that bitcoin had about a month ago were all down to centralisation.