Here is another long-held belief that I need to re-examine. My first serious shoot with my new D90 (at that time) was at the Andre Rieu concert and I was disappointed with the result. I mean, here I am with a spanking new camera that I thought was going to take me to new heights in photography. I thought I knew enough about how to get the most out of the camera. I set the ISO to max out at 800... after all the Dpreview website says the ISO in the D90 gets grainy beyond 800.
Again, I refer to Neil van Niekerk as my source of learning. Neil made a very good point: it is far easier to correct noise than to correct for camera shake in post-processing. By setting the ISO to as high as possible (within reasons, I think), it is possible to set the shutter speed high enough for a good shot. Unless you are shooting formal, any noise is usually not noticeable, especially when one seldom prints larger than 5"x7" for informal "happy snaps". On hindsight, I should have allowed my camera to go to maximum ISO and forget about graininess.
Here is a screenshot of the ISO's Neil has used in one of his wedding shoots. It looks as if he shoots at any ISO, and especially at 1600 (which I bet still looks good on his camera). It is worth noting that his purpose for high ISO is not so that he could do away with flash, but so that he could open the aperture wide!