Scyber, what is your theory for why Roku is not consistently appearing in Network settings?
First let me state that once again, this is merely a theory. I have not verified it nor even tested it. It is just my guess based on the behavior I saw.
The Roku implemented SSDP (simple service discovery protocol) in order to make it more easily discoverable for ECP apps. This is the same protocol used for discovery by DLNA/UPnP. The Roku announces itself on the network and gives a url that can be used to find an XML file that describes its services. That XML lives on port 8060 on the roku box. The file itself is in a DLNA/UPnP format with DLNA/UPnP values. The problem is that the Roku is not a DLNA/UPnP device so many of the urls listed in the file are invalid. So my guess is that Windows sees the broadcast and thinks that the Roku is a DLNA/UPnP device (adding it to the network screen), but then times out/errors out trying to verify the different features/urls. After it times/errors out, the listing is removed from the network screen. Since the SSDP broadcasts and response happen every once and a while on a network, the Roku may appear and then disappear from the network devices screen.
Once again, only a theory/guess. Don't rely on this for a definitive answer.