It was quite tricky to dig up. Found it by using tag search on "idol".
I believe that, one of the main reasons why "Sakura no Shiori" is doing this well is because it is bundled with four PVs and a bonus movie.
Atsuko Maeda is thrilled
:
http://ameblo.jp/atsuko-maeda/entry-10461437924.html
That entry has received more than 1,800 comments in barely two hours time.