Since I keep repeating this talk on not worrying about noise, I now have a longer story behind it
here.
Here's another interesting thing (more details
here): an example of how ISO 800 is better than ISO 400 (click on images to see larger):
ISO 400, pushed 1 stop in RAW processing:
ISO 800, ETTR:
Note the extra noise in the ISO 400 version in the dark ear area of the toy as well as on the edge of the toy in the top left area (you may have to click the images to see the larger sizes). This is why exposure is important. Focus is important because noise pops up more obviously in OOF areas (as can be seen on the periphery of the toy). And of course, if the composition isn't interesting, lack of noise won't save it.