The ribbon is apparently here to stay in Office, so your best bet is to get used to working with it. However, while adding the ribbon was one of the key features across the board in Office 2010, there is one application where it is minimised by default: OneNote.
OneNote has its share of fans at Lifehacker HQ, but just what did it do to qualify for such special treatment? According to Microsoft, the answer is that people found it "distracting" during testing (no news for me there):
Early product feedback indicated that you wanted maximum screen space for actual note-taking, instead of being overwhelmed by interface clutter. This seems especially important on laptops, Tablet PCs and netbooks, all of which typically have smaller screens.
If the ribbon gives you a similar feeling in other applications, remember you can minimise by typing Ctrl-F1 or clicking on the up arrow next to the help question mark on the right of the ribbon.
5 things you wanted to know about OneNote 2010 [The Microsoft Office Blog]