For those of you new to Dropbox:
“Dropbox is a Web-based file hosting service operated by Dropbox, Inc. which uses cloud computing to enable users to store and share files and folders with others across the Internet using file synchronization.”
Dropbox has become very popular and widely used as it has so many different uses and makes file sharing over the internet easy. Dropbox allows you to make public image galleries, share files publicly, share files between computers and manage version control. All this straight from your file system. I like to think of it as git or a subversion repository with a nice interface.