Always, if my lens is on the camera the lens hood is fitted, day or night (in the correct way, not reversed) always use Hoya HD filters as well...
I live in a busy city, the lens hood has taken quite a few knocks, seems to work as a nice buffer...also it is generally 90-95% sunny all year here, generally a harsh sunlight.
I always use clear UV filters, I'm not sure what it is, but almost everyday (after shooting) I have to clean off a flim of something/whatever, I assume it's due to the humidity and standard city dust/pollution.
I figure in the long run it is safer to be able to replace a filter than a front element..