Even as a seasoned webmaster and competent internet user with a Gmail account (capable of sending files < 10MB there are just some days you need more... I'm talking about sending those larger files, the ones that add up to hundreds of megabytes, videos, music, large presentations and other modern day content.
The hard part is figuring out how to send (or receive) large files from less experienced users. Sure, I can just FTP my files to a web server and share a link, I do that all the time, but I don't want to give out my FTP information to a low tech friend and it would be a real pain trying to help them figure out what FTPing is to begin with... that's where YouSendIt comes in.