This is something I do all of the time. Using Microsoft Outlook, I get an email from someone and need a reminder to call them. I manually create the task, copy/paste the phone number in and then delete the email.
Now wouldn't this be a killer feature...I right-click an email and have an option to "Create Task". This would bring up the standard New Task window, allowing me to define the task details with the email text included in the notes section. To make this even more "killer" I would be prompted as to whether I want to have the email sent to the Deleted Items bucket. I should even be able to make that a default setting.
Maybe this is already possible. You know, Microsoft says that 80% of the feature requests for Office already exist in the suite.