A screencast that demonstrates how Dropbox uses tricks to save disk space and bandwidth... and if it's already seen a file (even from a different user), it won't bother uploading it.
Read the full blog post here: fozworks.com/2009/12/19/dropbox-knows-quite-a-lot-actually
Loading more stuff…
Hmm…it looks like things are taking a while to load. Try again?