I found this short blog posted by exprodat GIS and thought it well done. Enjoy!
#10 is good... to a limit. A north arrow can also confuse or mislead depending on the projection used. For instance, when using a polar projection, a north arrow would look just weird. And when using an Albers projection for the whole North American continent, north is quite variable. The north arrow would only be relevant at one longitude. Certainly, many users are smart enough to figure this out... but, well, you get my drift.