If this idea is used please put my name (usagi) somewhere. Thank you.
From time to time, the network generates "imprint blocks" which contain two peices of info: A and B. A is either a common public key from which addresses can be matched, or a bitcoin address. B is the balance in that address.
At that point clients need only download in reverse to the most recent imprint block, unless they wish to obtain transaction history.
This is really what I see as the fundamental flaw in the bitcoin protocol, all transaction history is available, forever. With this new method the only important peice of info is the last imprint block. These blocks could even be produced daily if bitcoin took over the world.
Imprint blocks are as secure as the blockchain itself and would be signed (and sign future blocks) in the same way.
Since old addresses would always be carried forward there would no longer be a need to scan the blockchain. These imprint blocks could even be produced nightly by the devteam and included with new clients. Imagine the lightning fast startup times beginners would experience.
Anyway. Someone probably already thought of this, but imo it's the best idea yet.
AFAIK summary blocks are not possible because you need a full transaction history to prevent double spends...
