be aware that locking via HTTP is part of the webdav specification (rfc2518). There are recently a couple of new rfcs (and canididate RFCs) in this area such as rfc3253 (Versioning Extensions to WebDAV), rfc4709 (Mounting Web Distributed Authoring and Versioning (WebDAV) Servers), rfc4331 (Quota and Size Properties for Distributed Authoring and Versioning (DAV) Collections), and rfc4316 (Datatypes for Web Distributed Authoring and Versioning (WebDAV) Properties).
The goal should be to safely edit files in place. Here, WebDAV is certainly an important player, which is supported by more and more operating systems. Even, if you don't want to for some reason to use webdav in your requirements, whatever is done should be conceptually compatible.
