According to the Oricon Singles charts for May 10, the Hare Hare Yukai (ハレ晴レユカイ) CD single, ending theme of The Melancholy of Haruhi Suzumiya was the 18th best selling CD single in Japan for the day it was released.
Similarly to North America's Nielson Bookscan and Vidscan Oricon tracks sales at major brick and mortar music outlets. It does not track sales though online retailers like Amazon.com or niche market retailers such as the anime shops in Akihabara.
I really don't get why people are so batshit over the show. I guess it's cause every 10 minutes, Haruhi finds some way to violate, harass, or damn well gets close to raping Mikuru.
That + peoples odd facination wht the Mikuru Beam V_V