@morr: <sarcasm>Oh, so download.com have my nature photos that I've taken myself on their site and all those fun home videos? Wow, now I got to go there and look for awesome stuff!<sarcasm>
This is for all that small stuff like home made open source software shared with friends, your own photos and videos, maps you've made for games, addons and items for games, etc...
Everything you usually don't find websites for that would host it all for you.
Are you comfortable with using Imageshack.us for sharing your +1000 vacation photos, or do you prefer to put it in a folder?
It's for the kinds of things you don't want to upload to various hosting sites where you get various URL's to remember - and the storage is often limited as well as the downloads.
Oneswarm use torrents - just use your usual IM (MSN/WinLive Messenger, GTalk, Yahoo chat, etc.) to make sure you both are online in initial download, then your friend will be able to share as well when you are offline.
It's perfect for all those other stuff.