Proposed File API specification

Web applications should have the ability to manipulate as wide as possible a range of user input, including files that a user may wish to upload to a remote server or manipulate inside a rich web application. This specification defines the basic representations for files, lists of files, errors raised by access to files, and programmatic ways to read files. The interfaces and API defined in this specification can be used with other interfaces and APIs exposed to the web platform.

From File API working draft by Arun Ranganathan of Mozilla Corporation.

This API, if adopted by major browser vendors will allow client-side file manipulation and asynchronous uploads.

As far as I know, asynchronous uploads are only possible now using a combination of Flash and JavaScript such as SWFUpload. Flickr’s uploader uses a similar technique. Client-side file processing is impossible without a plug-in.