I wrote a small example on how to use dojo.io.iframe to send a file input via a multipart/form-data form in the background, using php as a backend:

http://dojotoolkit.org/~dante/upload.html
(link to php source on page)

it doesn't save the files coming in, more of a proof of concept, but a great starting point for something commonly done / needed. it only really requires core + dojo.io.iframe, as the indeterminate progress bar could be substitued with a sized div with the animated gif background.

I almost want to turn it into a widget mixin in FormWidget, like dojox.form.Upload or something, but for now it's just a dojo example, and a PHP example ... anyone interested in supplying examples for ASP / JSP / whatever - backend are free to post them here.

the first comment received was: "hey, it works in Safari 2.0.x!"