I have become a bit disillusioned at my camera's (lack of) ability to perform at higher ISO settings, and wondered if this is a general trait on low-end cameras, or is a Canon/Nikon 'thing', or perhaps my camera was just a Friday afternoon job and has a poorly performing sensor...
I have a Nikon D3000, and mostly used it at ISO 100 until recently, when I read somewhere that (some) Nikons perform better at 200 than 100. I switched to 200, and could see no obvious difference in quality under most conditions, so happily accepted the extra stop this effectively gave my basic kit lenses.
However, the other day I was trying to get some surfing shots in overcast but bright conditions. At ISO 200, I was metering at around 1/320 at the maximum f/5.6 I can get at 200mm stretch on my zoom. I wanted to get up around 1/1000 or better, so tried shifting the ISO to 400 and 800 to try them out. Even on the camera's screen, I could tell that the ISO 800 pictures were not worth keeping, and when I saw the ISO 400 pictures at full size on my PC, I deleted them in disgust as well. I was appalled at the drop off in quality even at 400, when the camera is designed to go to 1600 or even 3200 (Hi1).
I know it's really silly to compare them, but some pictures a friend of mine took with his 5D mkII at ISO 3200 in low light, came out as clear as anything my camera can produce even at 100, and even his Hi1 setting of 12800 is better than my 800. OK, so he has a pro-ish level camera, and certainly he has pro level lenses, whereas I have an entry level camera and very mediocre glass, but should my sensor really only produce acceptable images at ISO settings of 100 and 200 - perhaps 400 if I was desperate..?