Also, don't forget the many regional passes that are well constructed for visitors staying longer in one place/area. As Kallio noted, the convenience of more frequent services (ex. nozomi) should not be discarded lightly.

Ex. if you stay in kyushu for 3/5d , kyushu pass is much better (and cheaper) than nationwide.
Or, maybe, the new(ly named) JR Tokyo Wide pass for kanto area.
Or, Sanyo Sanin pass for your JR Sanyo needs (Kyoto-Osaka-Hiroshima-Hakata)

(I think) Full list of passes:
http://www.japan-guide.com/e/e2357.html

JR nationwide on the other hand is worth it for pendulum ( ) traveler covering different areas in few days (monday-fukushima, tuesday-hiroshima, wednesday-kanazawa, thursday-kyoto).
Finally, also note that some passes (not nationwide) are available for buying IN Japan the last minute if you don't want to commit before arriving (or if you are waiting for Mr Kuroda's easing).


ps. I've used nationwide, JRSanyo/Shikoku/Kyushu (not available now), Kansai Wide and next time I will try JR Tokyo Wide. It was very easy to calculate which pass was the best with a simple xls and hyperdia.