I’m a massive fan of WebDAV.
At Fuel Advance (the parent company behind projects like Tixi), we operate a small but highly mobile work force. We don’t have an office, and we need 24/7 access to our business systems from any Internet connection. VPN links are not an option for us – they suck over 3G and don’t work through most public networks.
Enter WebDAV. It’s a set of HTTP verbs which give you read/write access to a remote folder and its files, all over standard HTTP. The best part is that Windows has native support for connecting to these shares. Now, we all have drive letter access to our corporate data over the public Internet. It’s slim and fast without all the management overheads that something like Sharepoint would have dealt us. It’s also cross platform, allowing us to open the same fileshares from our machines running Mac OS X.
IIS6 had reasonable support for WebDAV, but for various (and good!) reasons, this was dropped from the version that shipped as IIS7. In March this year, the team published a brand new WebDAV module as a separate download. This module is built using the new integrated pipeline in IIS7 and is much more nicely integrated into the management tool.
Kudos to Keith Moore, Robert McMurray and Marchel Cohn (no blog) for delivering this high quality release!
Tatham Oddie 
WebDAV just sucks. It has no partial update. It has partial download, but have a 100 MB file on a WebDAV share and then update a single byte of it. Your computer must download the whole 100 MB, change that byte and re-upload the whole 100 MB. If you’d use a sharing protocol lie SMB/CIFS, AFP or NFS, actually a single packet must be sent out that makes the server change the single byte and that’s it.
For drive letter access problem…check this tfswshx.dll post for more info…