To the OP:
No more than I usually am. As it was said above, anniversaries don't matter. They could have blown up Denver yesterday, today, tomorrow, next week...
I will not live in fear. I will not spend today holed up in my house just waiting. I will live my life to the fullest and carry on with my daily business.
For the past several years I've had a constant heightened level of awareness. But that's because I have a better chance getting mugged on the light rail than getting blown up by a terrorist. You can't really prepare for a suicide bomber but you can prepare for an attempted mugging.
Stole my thoughts-before 9/11 we didn't think it could happen here,now we know better. As usual with the passage of time complacency takes over. Alertness/awareness is what we need to implement everyday but we also need to live our lives as OgenRwot said.
Don't pick a fight with an old man. If he is too old to Fight, he'll just kill you.