For a project we are implementing a WebDAV client library for talking to Sharepoint Portal Server 2001 and Exchange public folders. We did only implement the most neccesary things and skipped things like locking. We did not find a use for this functionalilty yet, and we are only implementing what we need. It's working pretty well.
We have great support for access to WebDAV search that we used for MacawDynaList, a document list viewer used for replacing all those lists in Sharepoint with something really powerful. The search has full support for paging sorting etcetera and can return results directly in a dataset so no transformation on the resulting XML is needed. Something else I really like is the easy of programming by mapping CLR types to the Exchange/Sharepoint WebDAV types. This makes it very easy to do proppatch/propfind commands and interpret the results..
Let me know if there is any interest in such a library. We use it for searching and publising information to Sharepoint and Exchange.