In every other rich text editor, Shift+ENTER = a manual linebreak*. In Outlook Mac 2011, of course, this doesn't work.
If I wanted a neutered email application, I'd use Mac Mail. I got Outlook because I *need* power: Expert use accelerators; ability to customize for my workflows & particular environment and style; automation of repetitive tasks that result from working at a 1,000-person company and receiving hundreds of emails (mostly useless) per day.
Expert efficiency is ground zero of HCI and interaction design, folks. If you don't remember this from your intro to HCI course, you shouldn't be allowed near an interface.
Bah!
* Context: I often have to email out lists of mockups / comps; I format them as a list (so people can refer to the comps by number in their responses) and find it more readable & courteous to my recipients to do something like this: