Off topic mostly when talking about 24-70's but, I think that a lot of people who say that IS/VC/OS or whatever you want to call it is useless are generally able to shoot with long focal lengths, with fast shutter speeds, up around 1/f or better. It is those of us who have subjects that require much longer shutter speeds that prefer to use in lens optical image stabilisation. Many of my subjects require shooting at less than 1/200, and I usually go for 1/160 as standard, sometimes I have to go right down to 1/60. I am usually shooting at 600mm, and using my 50D, I am usually also cropping one third of the length of the image too. This is the equivalent of shooting a full (APS-C) frame at 900mm or needing to use 1440mm to fill a 35m frame.
I believe, that stabilisation can be useful in any situation where the subject allows the use of relatively long shutter times. I know that I have a relatively narrow experience with stabilised lenses, but generally have not found any observable detrimental effects on AF, although I only have a 20D and 50D to base that on, using the original 100-400, and the Sigma 150-600 C. Actually as it seems to be much easier to keep the subject in the viewfinder correctly, AF performance seems better in the reliability stakes. Stabilisation is another really useful tool to have to make photography easier, just like AF in fact, again something which is provided as a tool to help photographers achieve better results, or even automated exposure controls.
Alan
