I found the following when I searched for 'MS-WebStorage' Apache Slide - Exchange 2003 - WebDav Request, which shows how he used the slide client to send a request to the Exchange WebDAV server. In the end, Slide was missing some functionality to be able to communicate with the Exchange server. Since we have control over the code, is there enough information in here for us to support the server protocol?
When searching for 'MicrosoftTahoeServer' in google, I got a lot of references to a white paper on making Sharepoint accessible outside the firewall (Microsoft TechNet: Deploying Microsoft SharePoint Portal Server ...). The reference was to version 1.0. Were you testing against our Sharepoint 2001 installation or the Sharepoint 2003? Also looks like a programmer from Hyperwave (a german content management company attempted the same thing in 2001).
As for fragility, it would be much more fragile for us to build our own client with extensions to the windows explorer.
I also searched for the header on Google and found some references to Exchange, in fact one of them was an admin guide for 'Sync4J connector for Exchange' which gives some info on how to update contacts and events etc. (like the guy was trying to do from Slide).
I'm guessing that all Microsoft's server products that support WebDAV support the 'MS-WebStorage' header.
This is all OK for Exchange but unfortunately doesn't help with Sharepoint as it is the POLL, SUBSCRIBE and UNSUBSCRIBE methods we need details on, which seem elusive!
I did the tests against activiti2 which I believe is running the older Sharepoint 2001.
You're absolutely right about the fragility, you just have to remember the old Desktop Client Explorer Integration at Documentum!!
What we need to do is try sending back the headers from our repository and see what WebFolders does, then just take it a step at a time adding more functionality until we get it working, unless you have a Microsoft insider that can get us some Sharepoint internal documentation John :-)