> Can nginx act as a front-end proxy for very long
> POST requests where
> the back-end server is not bothered until the POST
> is totally complete
> (at which point it is given the data).

It is exactly how it's done in nginx.

> Further, can it support (while the POST is in
> progress) another query
> as to the status of the POST (bytes completed,
> bytes to go).

Yes, using this module http://wiki.nginx.org/HttpUploadProgressModule