At last! Apple has released a Software Development Kit (SDK) for developing plug-ins for Sherlock 3. What this means (for non-developers) is that developers can now create Sherlock 3 channels. I'll let you know when I have a macosxhints.com channel! Find out more on Apple's Sherlock Developer page.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20021118060246312