The figures reveal a number of things. For one, Hanazawa Kana is extremely popular. For another, Mizuki Nana's popularity is undimmed.
Perhaps most surprising, the new seiyuu playing Menma in the current anime Ano Hi Mita Hana no Namae wo Bokutachi wa Mada Shiranai, Kayano Ai, has suddenly become very popular.
And my own current seiyuu of interest, Yuuki Aoi, is also of interest to many people in Japan.
Number of hits on Japanese Wikipedia, May 1 to May 21, 2011:
Cumulative number of threads on 2channel up to May 22, 2011, for that same group of seiyuus (each full thread =1000 posts):
Here we see Tamura Yukari's decade-long popularity showing itself. Horie Yui, just for interest, has 403 threads as of today. Hirano Aya remains of great interest to 2channelers, as a personality, if not as a seiyuu. And Asumi Kana has as many threads as Noto Mamiko, despite a shorter career and much less popularity among overseas anime fans. Her popularity stems from her moe-inducing character of Yuno in otaku favorite anime Hidamari Sketch.
I'll try to put together a list of the most popular seiyuus on 2channel long-term, but that will take some time. I'll just mention that Chihara Minori has 255 threads. And Hase Yurina (the former Ochiai Yurika) has 296, not for her seiyuu work, but for wild blog and twitter posts about her difficult life.
Actually, here is one more listing: the number of posts per day in the current thread for the top twenty seiyuus of interest on 2channel today. This ordering shifts a bit day by day, and I think gives a pretty good idea of who is currently in vogue. The first column gives total number of threads, the second the number of posts per day:
Here, what strikes me is the fact that Hirano Aya is such a continuing source of fascination, with both her main thread and her purely anti- thread in the top ten. Mizuki Nana gets a lot of negative comment, too, to go with all the positive comment.
Hara Yumi is a singer/seiyuu known for her work as Takane in the Idolmaster games. Nakamura Eriko is also in the Idolmaster games. Mimori Suzuko is also a singer/seiyuu and is in Milky Holmes.