Can I add a short comment to any email item and show that comment in a view? I don't want to change the subject.
Outlook's message flag feature is ideal for this task. In the folder view, you can right-click a message, choose Follow Up, then type text into the Flag to box in the Flag for Follow Up dialog box. You don't have to use one of the built-in choices, and you don't have to add a date. You can also flag an open message by clicking the Follow Up button on the toolbar.
After you've flagged some messages, you'll want to see the flags in your view. To modify the current view, right-click the column headings, then choose Field Chooser. Drag the Follow Up Flag to the column headings, and place it wherever you like in the list of fields.