Symptom
"Can't index" appears in the Index Status column of the Sherlock window.
Solution
This is the correct behavior for Mac OS X. As a multi-user operating system, Mac OS X enhances privacy and file system integrity by allowing each user to access only specific areas of the file system. Sherlock can only index folders or volumes to which you have complete access. By default, this includes your Home directory, and it may include other volumes, such as an external hard drive, to which you have write access. Sherlock cannot access volumes to which you do not have complete access, such as the Mac OS X startup disk, or to read-only volumes such as CD-ROMs.
Your Home directory should appear in the Sherlock window with a status of "Indexed". Volumes and folders which cannot be indexed will appear with a status note explaining why they cannot be indexed.