Hi Leon,
The answer in my case is both!
I have only had a few brief outings with my Canon 40D, but as it is not temperature regulated I have chosen to use ICNR to ensure that each light image is reduced by a dark immediately after the light exposure.
Also, I have noticed that processing the much larger .CR2 raw files in ImagesPlus and Photoshop take so much longer, so I am content at this stage in my DSLR career to do ICNR rather than suffer the burden of more post capture processing. It came as quite a shock processing images 3888 x 2592 at 10.1Mp!
With my trusty old SBIG ST7E it is quite a different story. With a chip size of 765 x 510 pixels the files are less that 1M each. Also, the camera is thermally regulated so it makes sense to capture lights and darks separately. The very tight integration between the ST7 CCD camera and the software CCDSoft also make it very, very easy to take separate darks and then perform the reduction later.
Cheers
Dennis