YouSendIt is one of a number of services designed to let you move large files (up to 2GB) between computers without wrestling with email attachment limits or setting up FTP servers. You upload your file to their service, users get an email notification, and they pick it up directly from YouSendIt.
Now there’s another twist on this (available at the $29.99 per month Business Plus level), called SiteDrop. With SiteDrop, you can embed the YouSendIt functionality directly on your own web site, to make it easy for business partners to send you large files. With SiteDrop, partners upload files directly to your web site (or so it looks to them) and you pick them up from YouSendIt. You can customize the form and get notifications of incoming files in a variety of ways. Looks like a nice solution for folks like web design and development firms who need to swap things with clients who are less tech-savvy.