UPDATE: Amazon S3 now supports Cross-Origin Resource Sharing so HTML5 uploads should now be possible. See the docs here: http://docs.amazonwebservices.com/AmazonS3/latest/dev/cors.html and the original post here: https://forums.aws.amazon.com/message.jspa?messageID=377271#377271
Sorry, but Amazon still does not support HTML5 uploads because they do not support the Access-Control-Allow-Origin header. It's been 2 years and there is still no progress from Amazon in regard to this issue.
The old method of hosting an iframe form in your bucket only works for HTML4 uploads, not with HTML5.
More info here:
https://forums.aws.amazon.com/thread.jspa?threadID=34281
Also, more info from the Plupload guys here:
http://www.plupload.com/punbb/viewtopic.php?pid=2361#p2361
If you want to upload a file to S3 using a standard file input field, I would recommend reading this tutorial... otherwise you'll have to use Flash, Silverlight, etc. to upload.
http://aws.amazon.com/articles/1434?_encoding=UTF8&jiveRedirect=1
