Seems a bit similar to http://ge.tt/ - They also feature a drag-and-drop uploading, with 2GB for free, user registration and an API with wrappers for a few languages. Two features from them that you should maybe consider is a) to automatically start uploading when files are dropped on the site and b) if no file has been dropped on the site and the user clicks the upload button, present them with a file chooser.

Otherwise, nice job. I like the simplicity of the design, but it is a bit bottom heavy because of the big, black button.