Thanks for all the good replies! I would return no later than the 20th, as family thinks PHX is warmer than most other places in our country for Christmas. Seeing the museums is high on the list, and figured that was pretty weather-unrelated. It's good to hear they're less crowded.

Given the sad events of this week, I've decided to hold off booking for a week or two to see how things shake out. I'm not so concerned about terrorism as I am about logistics--delays, changed flights, etc. I suspect, though, that the ripple effect from this will be months and years rather than weeks.

JP