A nosy -- but helpfully so -- reader scrounged around the iTunes package files and discovered an image in the Help directory (/Contents/Resources/English.lproj/iTunes Help/gfx/) called "ringtone.gif." The image is a plus sign next to a bell -- add a ringtone, anybody? This helps confirm disputed reports that you can actually add custom ring tones to your iPhone.
For the record, this doesn't mean the feature actually exists (yet) in iTunes -- just that it's likely, if not now, then in a future update. Guess we won't know 'til 6ish tonight.