David - I had something similar happen to me when I was working with some IR film in England.
I had just started playing with IR and was hedging my bets a lot. So I would stop all the way down for focus, put on the filter, rate the file as 12, and start bracketing like mad. I mean like 5 stop brackets here.
I was taking one shot of the ruins of an old abbey. In one corner I ended up with this ghostly image of a woman standing there and then turning away out of the frame. It must have been a pretty quick turn because I don't think I got below 1s for that exposure, but it lent a nice ghostly touch to the image.
Now if only she could have been in period costume....
I will say though that regarding "the curious" it can be useful to look for vantage points which aren't that noticable. I saw a great picture on PNet of Camden Market taken from a roof-top or window overlooking it. The long exposure caught thebustling of the market really well. And there were no "stand outs". Something to consider.