I had been trying to figure out how to get Chatter notifications when a new case comment is added to no avail until the following solution dawned on me. Feel free to use it, share it, etc.

"Case Comment Chatter-er"

1. Create a field on your case page titled "Last Case Comment Date/Time" of type "Date/Time". Don't add it to your page layouts so it is basically hidden.
2. Create workflow rule named something useful such as "Note Last Case Comment Date/Time"
3. Object: Case Comment
4. Evaluation Criterea: When a record is created, or when a record is edited...
5. Rule Criterea: "Case Comment: Body not equal to null
6. Create field update on the Case Comment object that set the value to "NOW()"

Basically, whenever a case comment is added - this workflow will trigger and set the Case field "Last Case Comment Date/Time" to the current time. You can now follow this field in your Chatter configuration and get alerts whenever a comment is added!

Sweet.

Thanks,
Josh Lipton
Advantix Solutions Group