David over at Geeks are Sexy has a nice tutorial on keeping WordPress installations current by using Subversion to check out the latest code directly from the Automattic repository.

David’s instructions are much more detailed than the brief steps provided on the WordPress site, and also describe how to check out stable WordPress versions as opposed to the latest bleeding-edge code from trunk, and how to switch an established blog to Subversion to facilitate future updates.

(Essentially, you check out a working copy to your webserver via SSH and reconfigure the fresh install to use your existing database content — worked here quite nicely.)