TitanFile is great! They also sent an email out to customers this week with a preview of their new version and it looked like it had a much nicer UI as well.
TitanFile solves the problem of secure file sharing and tracking (accountability) as the data is secured end-to-end, there is notification of receipt/download (who accessed the files, where from, at what time etc) and ability to set files as read-only (access only from the browser window over SSL connection) as well as verify identity of recipient before giving them access to the files (2 factor authentication) without requiring recipient to have a TitanFile account.
Dropbox kicks ass as "file system of the internet" but sharing files with people in a secure and private way with dropbox is a big pain.
With next release we will integrate with dropbox and Google Docs as well.
Disclaimer: I am from TitanFile