There isn't much to say except that this won't stop big running events, Boston, or the U.S. from what it loves. Thoughts of course are with the victims and families. We'll find who did this.
Monday night with friends I went out for a Boston solidarity run in Poway. And in that vein, many SD runners will be doing the LJ Half that's coming up, and I imagine there will be a moment of silence and/or a huge cheer at the starting line for Boston.