12 years ago that I stayed home from work so I could be at my FLGS to buy a copy of the new D&D 3rd Edition Player's Handbook.
Sorry if I choose to be selective on how I remember this day.
In truth 9/11/2001 was also a watershed date for me personally. I had just gotten laid off from my "Dream job" in the Dot Com world (they had laid off 65% of their workforce that day). So I was home with a new baby when all the events went down.
I then spent the next few months (before I swallowed my pride and went back to teaching) working on various RPG products. One, the Buffy the Vampire Slayer RPG, lead to many, many other projects that eventually landed me Ghosts of Albion.
Since 9/11/2001 was 11 years ago, it was also a Tuesday when it happened (perpetual calendars are 11 years long), so to me the "big anniversary" of something is not 10 years, but 11. Weird I know. But that is why it is on my mind more today than say this time last year.