Re: File API Feedback

http://code.google.com/apis/gears/api_blobbuilder.html

> This I'm less sanguine about, since the immediately desired capability is>
to work with existing system files.
The motivating usecase for this feature in Gears is to compose the body of a
POST in the multipart/form-data format, including binary file parts. The
resulting blobs can then be uploaded with HttpRequest. For example, Gmail
uses this when sending/saving messages with attachments that had been queued
for delivery while offline.

Does the FileAPI + XHR2 provide for anything like that?