Obviously, our hearts go out to those injured and the families and friends of those killed. I also feel for the runners who trained for so long. I've never run Boston but I have run 9 other marathons and I can only imagine the sadness and frustration they must feel.
In 2001 I was working for a consulting company and at that time was flying internationally about 300,000 miles per year. Shortly after 911 my company communicated that if we didn't want to we would not be forced to fly to our consulting meetings. Though the idea of flying at that point was fairly scary I refused to be stopped from doing my work and I was on the first plane to Europe. I refuse to let terrorists (domestic or foreign) stop me from living my life, contributing what I can to the community in which I live, and doing the things that I love. If I had run Boston this year I would absolutely be back next year.
That's my middle-finger to whomever planted those bombs. Boston, I'm with you.