I haven't seen it encouraged, but when the space shuttle Endeavour made a stop 2 miles from my house on the way to California, I saw quite a few people biking to go see it, seeing that the traffic was at a standstill through much of the afternoon and evening. At the time, my bike was on order, but not in yet, and dh REALLY regretted not having his old steel roadie in condition to ride down there to see it. He ended up seeing it from a distance early the next morning, before it left, but he wasn't able to see it up close because the traffic was just that bad.