One of my favorite keyboard shortcuts in PowerPoint is Shift-F3. It rotates the capitalization of the current word among lowercased, Capitalized and UPPERCASED. Note that you do not have to select the word, and the cursor does not have to be at the beginning of the word either(*).
But the title of this post clearly said Emacs, didn’t it? Well, since I missed this feature in Emacs, I just implemented it in a pinch and bound it to Shift-F3. 
The code is in this page in EmacsWiki. I have only tested it on GNU Emacs, and so I can only hope that it works in XEmacs.
(*) Actually, you rarely have to select a word in PowerPoint in order to format it. Commands like Bold Ctrl-B and Italic Ctrl-I will act on the current word when there is no selection. Also, similar behavior is in fact present in all Office applications. I just picked PowerPoint.
