I'd like to post a suggestion for those who are about to download the torrent blockchain and who care about their existing fine torrent ratio in their old torrent client:

With such a huge download (21GB right now), any sweet torrent ratio will inevitably get borked quickly (depending on how many GB you had uploaded previously). To save your old nice torrent ratio, consider getting a new torrent client (preferably a "portable" one) and use it only for downloading the blockchain. When you decide to seed it (either part of it, or 100% or more of it), you can load it in your old torrent client, and even improve your old ratio quite substantially by seeding that huge database.

I wish I had done it like that, before I fucked up my cute old torrent ratio with this blockchain torrent. ;-)