Your answers are encouraging so far. I have looked at the Google Products forum, which is quite sobering and has discouraged me from buying the N6 at this time. However, I'm trying to get an idea of what the odds would be that I would get a phone with the random reboots. Several people have reported getting more than one defective phone when they return it. That would be aggravating. OTOH, I come here and read about a lot of people who are very happy with their N6s. I have been seriously considering buying something other than the N6 because of the random reboots, but it would not be my first choice. I'm trying to calculate how much of a risk it would be to go ahead and get the N6 and see what happens.
I presume that if I got one that was rebooting and had it replaced with another that had the same problem that at that point I could choose to return it and get something else. (I would be buying from a carrier---AT&T---on a two-year contract.) But that's only if I decide within the fifteen-day period, right? So if the problem showed up after fifteen days I'd be stuck with the N6 and, possibly, multiple exchanges during the warranty period to try to get one that works properly.