With a slight tweak to the Bitcoin protocol, it should be possible to shrink the blockchain to a much smaller, more easily usable size.

The Bitcoin blockchain is the ledger of transactions done with Bitcoin. It is used to verify the credibility and truthfulness of EVERY Bitcoin transaction done. It eliminates double-spends, and confirms transactions. Its size has grown, as of this writing end of April, 2014, to more than 20 gigabytes of disk space on your computer, once you have it fully set up. To set up Bitcoin on your computer and download the entire blockchain, might take takes days, and and does take tons of bandwidth through your ISP, if you download it directly through the Bitcoin computer program. (NOTE: there are Bitcoin wallets that work perfectly well without downloading the entire blockchain.)

The tweak to the blockchain would be to include only the first time every Bitcoin address showed up in the blockchain, and the last (current) time. This would eliminate a whole lot of transaction info that had long been completed, useless info except if you were a transaction tracker. Not only would this save download time and disk space, but it would mean that anybody who wanted to track the flow of certain bitcoins would have a much more difficult time doing it, thereby increasing anonymity. Even the NSA would have to work a little harder for their money.

Perhaps some of the new altcoins (alternative coins to Bitcoin) might be incorporating this feature into their blockchains.