This may sound extreme, but I always turn my computer off at night, or when I leave the house with no one else at home. The reason for this is because one time I went to the store, which was right across the street from my house. I returned home to the smell of something electrical burning. I was horrified when I isolated this smell to my computer. As it turns out, my CPU fan died, and of course, we all know how devastating that can be.
Fortunately, in this instance, I was able to shut the computer down in time and the CPU did not suffer damage that I could tell, but ever since then I decided that I was better to shut it down than leave it unattended for an extended period. I've never had a problem since.