Left in colour it wasn't too intrusive & only very obvious when you enlarge shot to 100% view in PS. I think for portrait work it can work quite well, especially if throwing the background out of focus.
I tried converting to Mono & then it really did show though. Colour is obviously more forgiving in this area
If I had to shoot at high ISO consistently I would have gone the Canon route....I have discussed this with Steve & seen some of his examples, which shows how well the Canon copes with it. For me though it will be very rare I shoot at this ISO, so other factors kept me on the Nikon route.
How are you finding it out in the field ?