I remember the exact moment I heard he had been killed. That definitely was one of those "Do you know where you were the exact moment when..." moments.
I was in high school at the time, and had just woken up to get ready for school, when I heard it on the radio. The news filled me with an incredible amount of sadness.
Lennon truly was an artistic genius, and the world is that much less colorful because his life was cut short at such a young age.