I just read 'There will come Soft Rains' with a group of students a couple of days ago, and an interesting (and rather obvious) issue came up in our discussion. If the house is so hyper-aware as to immediately clean up a speck of dirt, why is it unaware that its human inhabitants are no longer 'at home'? Is it simply a malfunction? One student (quite cleverly) suggested that the house is "in denial" (!), as it behaves like an obsessive person who refuses to see the obvious truth - a thoughtful, if questionable, theory (the house is so deliberately unemotional, artificial and UN-human).
It was also interesting that for a generation who have not lived with the direct threat of nuclear war, the image of the atomic shadows on the wall of the house is no less striking and haunting - testament to Mr Bradbury's power to touch readers in timeless and universal ways.

my first reaction was to agree with the "in denial" theory, but i think the house may not have been programmed to run if there were no humans in the house. Also, without the humans, the house really doesnt have a point, it would be dead without them. Nothing wants to die, so it could be running just to have a purpose.

Yes, but is the house in fact self-aware? Isn't Bradbury's point that technology can superficially imitate humanity, but it cannot BE human?

The interesting thing is that today (in 2002), we actually have "smart homes" in which a central computer can be programmed to lock and unlock doors, turn lights on and off, turn on a coffee-maker in the morning, etc. They can be programmed in several different fashions, from a Monday-through-Friday schedule, with a different one for Saturdays and Sundays, to a completely different schedule for vacations (and even simulate a "lived-in" pattern of lighting use to fool would-be burgalars).

Presumably, the house in Bradbury's story only has the limited intelligence to follow the programming pattern set in its memory before the nuclear attack took place -- and so it continues to follow that same program even though the people are no longer there, as it would until someone reprogrammed it for a different pattern of actions, or in this case, until the system breaks down entirely.