I've tried looking for something exactly like this before to no avail. Really awesome assuming it can deliver!
That said, being more transparent in the Readme on Github about the browsers that are currently supported and that plan to be supported would be appreciated. Blob is only Chrome 21+, Firefox 13+ and IE 10+ according to MDN (https://developer.mozilla.org/en-US/docs/DOM/Blob), and judging by the "FileBlob API is not supported" comment under the TODO section, there isn't any backwards compatibility yet. How far back are you planning on supporting?
Really glad you find it useful, and you're completely right that I need a section on compatibility. The nice thing is that for browsers that don't support Blobs, Amazon allows you to just upload the file as one giant chunk with the same multipart API. I'm not absolutely sure yet (I still need to do some testing), but this should mean that browsers versions as far back as IE 5 will work - only basic XHR compatibility will be required to function. I'm planning on covering as many browsers as possible, I just haven't found a great way to go about this yet. Is there a better option than http://spoon.net/browsers/?
That said, being more transparent in the Readme on Github about the browsers that are currently supported and that plan to be supported would be appreciated. Blob is only Chrome 21+, Firefox 13+ and IE 10+ according to MDN (https://developer.mozilla.org/en-US/docs/DOM/Blob), and judging by the "FileBlob API is not supported" comment under the TODO section, there isn't any backwards compatibility yet. How far back are you planning on supporting?