With how computer are now a days(sleep mode or hibernate) i see no reason to shut them down every day. I personally think shutting your pc down every night is hard on the hardware, but you can also go the other way and say that leaving a PC on all the time is hard on it as well.
I think it is a matter of opinion, and the users preference.
Very true. My county actually requires all the schools to shut down their computers every day to save money on energy. In my engineering program at one of the high schools we have about 80 desktop computers running throughout the several classrooms. We used to leave them on, but now we shut all of them down. The county says it'll save close to $100,000 dollars by initiating this at every school. I guess you don't have to worry about money when you only running 1 or 2 computers in your home... but on a large scale it makes a difference. As far as how it affects the computer hardware, I agree with Stang02GT. It's a matter of opinion. I haven't really done any research to see what is better for your hardware, but I've got a good bet that someone out there
has researched it and posted their findings on the internet. Google it!