My daytime shots seem to come out fine no matter what ISO I'm using (I shoot a lot more film than digital, if that matters), but in low light, the lower ISO's get really noisey.
P.S. I've been shooting pictures for a lot of years, but I have absolutely no formal training, so if I get teminology or technical stuff wrong - please correct me. I generally try not to get into technical discussions, due to my limited knowledge. I know how to make my camera (an old AE-1, by the way) do what I want it to - most of the time - and that's all I need.