Thank you for contacting Clarizen Support.
Please correct me if I misunderstood, but I think you are referring to 2 separate things.
1) When you go to timesheet and click on Export, you are exporting a current view to Excel. You can customize it according to your needs and add or remove additional columns/fields. Simply click on Gear Icon > Manage. See link: http://screencast.com/t/RZNmCQiVrnu.
2) To be able to run a User's Hourly Summary report that includes comments, please go to Reports module > Resources Hourly Report > Run and you should be all set :)
Please let me know if this answered your question.
All the best,