I first heard of Touhou when one my fellow piano students suggested a duet version of Cool&Create's U.N. Owen Was Her? mix (from the exact video Seamus posted a page ago) for a performance piece. So we did, and it was awesome. The basic background research on the song gave me only the name of the game, "Embodiment of Scarlet Devil," which gave me a really inaccurate picture of the nature of the series.
A few years afterward, I ended up finding more of the music, then got on a listening kick with some piano arrangements, and got so hooked on the music that I learned a bunch of it for piano. Then I downloaded EoSD to try it out, and I kinda fell in love with it on first play.