Magento Request - Frontend or Backend?

Question

How can I tell if the current request is for a backend or frontend page? This check will be done inside an observer, so I do have access to the request object if that helps

Answer 1

Whether I'm wrong or not (but I've tested it), some events (like controller_front_init_before) can only be overwritten inside global node. As a result, this override will affect both frontend and backend.

Then come Alan's and benmark's solution to the rescue to specify if you want to apply the observer on frontend only or backend only.