The mini toolbar appears as you select and hover over text, or right click text in a document. This provides a handy font menu for changing the selected text. One of my favourite things about it is that it gets more or less transparent the further you move away from it, as if to say “you need me? oh, ok, I’ll get out of your way”.
Of course, you can banish it altogether - If you do not wish to use the mini toolbar, it can be disabled by:
STEP 1. Select Office Button | Word Options Button | Popular
STEP 2. Deselect the Show Mini Toolbar on selection option
STEP 3. Click OK to save
Note the mini toolbar will be disabled for hovering over selections, but will still appear if you right click.
The minitoolbar is an example of good design. It's always been there, I've used it, but I've never even thought about it. Until I read your blog post, I didn't realize it existed =).