I'm another person who doesn't use Twitter, however I do have an account. And frankly, I fail to see many use cases. But I also acknowledge that the few use cases are powerful.

     1. On the ground reporting
     2. Messages to group of friends, like where to meet
     3. Coordinating group efforts outside friends list in X social media
     4. Warnings related to specific area/time
     5. Error logs related to web services
     6. Command/Control of hidden machines
     7. Complaints to companies with sensitive web presence