Every item on archive.org has a bit-torrent file, I believe. This doesn't solve the problem of working out which items are the most popular, but if you can figure out that then you would be able to manage storage and bandwidth. I suppose the real question is: how many other people use bit-torrent to download from archive.org, as opposed to direct downloads. I (sadly) suspect it's a very small fraction.
Semi-unrelated, but if you're looking for ways to help and have a spare server, Archive Team [1] is always looking for additional capacity. Although Archive Team != archive.org, they do grabs of at-risk content which (almost always) get uploaded to archive.org. [disclaimer: I help out with various Archive Team projects, the most recent of which was the backup of Yahoo Groups).