I posted the following poll on Facebook and thought the responses interesting enough to summarize here.
Here is a summary of the results:
A strong majority of folks print overnight without concern. Another pretty large group prints overnight but with some concern. There are a fair number of folks that do not print overnight but the survey questions are flawed in that these folks could have reasons other than fire concern.
Some other observations. There are a number of people that have added fire detection and suppression with a variety of solutions mentioned from off the shelf, to external service provided, to self crafted. Finally there were even folks that admitted to having their spouse or boss tell them to pound sand on the printing all night thing. My other survey question asked if people had experienced a fire. A very large majority had not though a handful did. The fires described were all minor. Probably a bad survey question as someone that had a bad fire may not be doing the whole 3D Printing any longer! Finally, from comments on both polls, it seems like the concern is the highest with the cheap home built printers and diminishes as you go up market.