I can't tell you how many times I have found a portal comment that needs to be internal. I have to open the comment, copy the text, create a new internal comment, paste the text, save it, then go back to the original comment and delete.
You can now give portal users the option to comment privately. These private portal comments can only be seen in the portal by your internal portal users. Hopefully this will reduce the need to turn portal comments into internal comments. You can learn more in today's blog.