By Mark L. Chambers from "Mac OS X Lion All-in-One For Dummies"
Mac OS X provides you with a Spotlight Comments field in the Info dialog, where you can add additional text that’s stored along with the file (and can be matched with Spotlight). You can use this feature to record the version number of manuscript chapters during the course of writing your next bestseller.
To add a comment:
1. Display the Info dialog for the item by pressing the Apple command key+I or choosing File—>Get Info.
2. Click in the Spotlight Comments box and type the comment text.
If you need to expand the Spotlight Comments section of the Info dialog, click the triangle next to the Spotlight Comments heading. The arrow rotates and the Spotlight Comments box appears.
3. Close the Info dialog to save the comment.