Just wanted to share the following information with folks.  There is another PC user who led the way on this, but there is no information here on the forum that discussed their successful efforts, which we then expanded upon, so I wanted other merchants to know about it.

Also, this is by no means intended to be a pitch for the service provider I'll refer to, but as an acknowledgement for Early Impact's implementation of the XML SDK because without their foresight to build that tool, this little project would simply not have been as easy or practical to accomplish.  I will note, however, that the fellow at Webgistix who accomplished his end of the integration (he really did most of the work - I just directed him a bit) is quite competent and responsive, and I felt he did an exceptional job in performing his role in the project.

http://www.webgistix.com - http://www.webgistix.com is a warehouse / order fulfillment service.  My client found their way to these folks and agreed to warehouse their products with them.  They require that orders be transmitted to them electronically, and the drop-ship purchase order e-mail was not an acceptable solution to them.  They wanted the data passed to them via XML.

In PC admin, we simply created a XML partner id and provided that information to Webgistix.  At their end, Webgistix has a VBscript which was developed while working for the other PC client that blazed the way on this.  We helped Webgistix refine that script so that it would discriminate between live orders and other (such as test) orders, based on order and payment status codes.

The VBscript pops up occasionally (every couple hours), querying my client's site for new orders.  Their script automatically detects the new order and introduces those orders to the Webgistix system for further processing and shipping. 

Webgistix also has an API that could be implemented for situations where immediate pass-through of orders (rather than waiting for the VBscript's next cycle) is desired.  We chose not to go that route at this point.

Anyhow, that's the story.  Time will tell as to how these Webgistix folks operate, and so on, because we literally got this working in the past week and there isn't much of a track record yet.  But for merchants looking for someone to warehouse product and to ship order, who just happens to be fully integrated with ProductCart, this might be a nice solution to investigate.