I do know a fan of Japan isn't necessarily a fan of anime. But when you get in a bookstore in Japan, you'd notice there are so many piles of anime magazines and manga. I grew up watching anime, but there are so many series these days that even I get confused.
There is a convenience store in Japan that is called "LAWSON", and it was selling K-ON related merchandises until the last Monday. You can click this, and see it's advertising K-ON. And I got this coffee just to show you.
I was embarrassed when I showed this to a clerk to buy. Even though K-ON is as successful as Lucky Star or Haruhi, I doubt it's known to many Japanese people. You can download K-ON voice ringtones by visiting the URL on the cup, but the site requires certain procedure that would be too complicating to understand for non-native speakers.
Sorry if you don't know much about Japanese anime. The taste of the coffee was way below my standards....>.<