If this idea of identity was integrated with FB I think that would be a huge win and a ton of different programs could hook into the keybase API for automatic behind the scenes encryption that would prevent a lot of issues surrounding dragnet surveillance.
There's also the technology to make it far simpler, in the form of Namecoin. I've registered a NameID (in the id/ namespace), and I can tell anyone in the world that my NameID is vshell. They can look me up, find my GPG key, my website, and whatever other information I want to put in there. Nobody can fake it.
The main issue is going to be revocation - if someone manages to take control of my NameID, I can't get it back. I can use multi-factor authentication like BitGo provide for Bitcoin, but that's not a 100% guarantee. I could sign "I am no longer this person" with my NameID key and my GPG key and distribute that, but there'd be no safe way to say "I am now this other person", because they might've taken my GPG key as well and they could say that. You're essentially going to have to build up your web of trust from near-scratch, starting with physical trust (i.e. people who can verify who you are physically).
It does not prevent (although it does make it much harder) impersonation through key theft.
*: profiles adding 100 "friends" the first day, using pictures from obscure russian models (which can be found using Google image search)...
I think the DEA could have faked it, even if there were strict measures.
But think of what average people are doing right now using similar techniques... The public is blind to this but the technology (GPG) exists to authenticate people's identities.