This allows:

* direct S3 uploads (no need to pass through your server)

* async uploading with progress bar

* pre-upload client side image resizing to reduce upload time

* post-upload server side on the fly image resizing for easily generating as many thumbnails as you wish

It's been helping me a lot lately and I felt I should post about it.

You can see it in action on www.boorgle.com on the edit profile page after registration. The initial loaded background photo will be server-side resized depending on your browser window size.