Pojo - When uploading an image, the picture is shown immediately with an upload progress overlay.
Dropbox - When sharing a font using the web interface, you can customize the font preview.
/via Sohrob Nayebaziz
Google+ - When uploading an avatar that does not have a face, a notification suggests uploading a more recognisable photo of yourself.
/via Brian Grellmann
Flickr - The favicon turns into a live indicator showing the progress of the upload.