The unspent transaction outputs (UTXO) is the actual distributed ledger. They are contained within the journal of all transactions seen on the network (the blockchain) which needs to be sorted through and filtered for unspent outputs.

You can tell all the "blockchain tech." was a bunch of marketing BS spouted by followers, not leaders, because the blockchain is already obsolete. UTXO is the future and where all the bleeding edge development is happening.

actually, pruned nodes can't interact with SPV clients since they won't have the blocks. 

SPV clients use a bloom filter looking for the addresses and transactions they are interested in to the peer. The peer then only includes the relevant transactions in blocks it returns, together with their Merkle paths to prove that these transactions were indeed part of returned block.

UTXO's have always worked this way; throwing away the spent ones.  The UTXO set is very small compared to blocks because it only contains info on unspent data and doesn't contain any signatures or data, thus, this is not what results in less storage.  it is the discarding of old blocks.  in the case of saving the last 2016 blocks (minimum 288), 351874 of them as of now.

Yes, keeping whole block ranges (randomly determined before pruning) is an important feature of pruning which will hopefully be included in due course.

Not exactly. BitTorrent distributes the entire file to all peers and in fact it actively tries to distribute pieces with a low count more quickly. In this case, not every node would have every block by design. It's a bit more dangerous what is being proposed. An attacker can prevent new nodes from syncing by finding all of the nodes that have a particular piece of the blockchain (whichever piece is rarest) and attacking them.

Still, as long as there is one good copy of the blockchain in the world, it can always be sent out again. So I don't think we need to worry too much. Some people will still run nodes without pruning.

starting to roll:

So what  do all these pruned nodes do with the blocks they mine going forward? Immediately delete them after they get accepted into the longest chain?

Oh fuck indeed

No, unless you can verify the flow of transactions yourself you are ultimately trusting the miners. They put the transaction in the block; the hash proves that. But how do you know they were not cheating when they did? Also, you don't know that they didn't prune something they shouldn't. Maybe you got a payment, and the miner doesn't want you to see it (or the government told him to remove it), so they prune it (retaining only the hash, but the block is still valid).

Satoshi's pruning is basically the same in terms of trust as SPV.

The current pruning scheme that is implemented compromises nothing in terms of trust. You receive the entire blockchain and verify it completely, but you only keep some N recent blocks (or maybe specified amount of storage? i'm not sure). It uses the same bandwidth as before, but less storage.

This doesn't really address where those old blocks will be stored, so that is being worked on as discussed in the last several posts.

If you want to reduce bandwidth you are going to end up with various weaker models in terms of trust because since you aren't receiving the entire chain, you obviously can't verify everything yourself. You end up needing to trust somebody somehow.

SPV is fine for end users, and it has pretty much the minimum possible bandwidth usage. It does have some privacy compromises because you have to tell the nodes which addresses you are interested in (or at least a superset of that).

Satoshi's pruning is ultimately similar to SPV in terms of trust (you are trusting the miners) but has intermediate bandwidth usage (less than full trustless verification and more than SPV) and unlike SPV does allow mining.