I hadn't gotten around to noticing myself so I just learned from this hint at Mac OS X Hints that Web Sharing is no longer available in Mountain Lion. Web Sharing enables the use of the Apache web server built in to the OS. If you need to get Web Sharing back on Mountain Lion the above mentioned hint contains some links on how to do so.
Unfortunately, the script Re-Add Selected Tracks as Podcast requires Web Sharing be activated, since it uses the local server to re-import files as faux RSS enclosures. So if you want to continue using it on 10.8 you'll have to restore Web Sharing.
Update: Topher Kessler has a very good Web Sharing restoration tutorial at CNET.