WebDAV folders allow you to manage your webserver by looking at familiar folders, instead of via an FTP client. Now you can drag and drop updates to your webserver very easily.
Here's a great tutorial on how to make them work:
[This link no longer works, but the comment to this article contains a link to information that does work in 10.2 and newer...]
First noticed on MacNN, posted by Tom Benarz.
Mac OS X Hints