Originally Posted by
Ákos Lumnitzer
Yes, ISO800 is very noisy if you use a simple point and shoot or some of the lower end camera bodies. The mid-high range bodies all handle noise relatively well at ISO800. I have an "old" EOS 30D and ISO800 is generally my choice of ISO nowadays for getting fastest possible shutter speed as often I shoot in areas with lots of trees and shade. When in the open and good light I will drop back to ISO400, sometimes even lower. I think my camera body would lock up if I suddenly picked ISO100 :D as I think in three years of use I would very, very rarely have selected that setting.
Nikon's new top end camera bodies are incredibly good at even ISO3200 and higher.
What Ilija said about overexposing is spot on. your review images on the camera screen will look overexposed and crummy, but checking the histogram and seeing it pushed as far right as possible will help minimize noise.