I'm not really into the whole Vocaloid thing, but I remember there was something about a CD of Vocaloid music topping the charts there last year or such. A little Googling comes up with this excerpt:
http://myanimelist.net/forum/?topicid=211424
Granted, it was only for one week, but still considering the "singer" is computer-generated, it's interesting.
"According to Oricon news, VOCALOID Hatsune Miku's album "EXIT TUNES PRESENTS Vocalogenesis feat. Hatsune Miku" has won the top in the weekly album CD sales ranking for May 17th - May 23rd. It's for the first time that a VOCALOID CD is ranked first in the weekly CD sales ranking. The album also includes the songs of other VOCALOIDs such as Kagamine Rin, Len, Megurine Luka, Meiko and Kaito. The cover illustration was drawn by Miwa Shirow.
Note that the sales of the CD, 23,000 copies, are the smallest number in Oricon's history among all the top sellers of the weekly CD rankings, reflecting the shrinkage of the CD market in Japan."