I have many routers in use and have always suffered from rebooting problems. I have one site that reboots very often, and can narrow it down to certain users being online at that time. I have tried 5 routers in the same place and they all do it. It isn't memory. It is not temperature related, and reducing CPU clock frequency has no effect, nor does turning off wireless or replacing the power supply help in any way (I don't use wireless on the routers).
So, what is it?
It appears to be nothing more than the router suffering from rapid connections storms (DOS) on most occasions, this could be from P2P apps or virus/malware - but this happens so fast that usually we see nothing in the logs and are unaware of what has happened. What, if anything, can be done about this, is the question. It shouldn't happen. There has been much discussion of this on linksysinfo.org. Recently, there seems to be a new bunch of viruses going around, and this is becoming more of a problem.