It took me a little while to get used to it. Initially I found the grey and the overall lack of contrast hard to come to terms with, but I have got used to it and I thought it somehow looked ‘cheaper’.
Interestingly when I went to do some work on a clients system and they still have Pro Tools 7 and the thing that struck me the most was the thickness of the automation lines. In PT7 it looked like a massive marker pen had been through my edit window when I was in volume mode. 
Also I initially was concerned that the contrast for highlighted regions wasn’t great enough but I haven’t found I am struggling to find the highlighted region.
I do find that the PT8 look is more restful on the eye. I do like the new toolbar and the clearer buttons although it is taking me a while to get used to the different locations for some of the drop down menus like the Region List one as I am so used to clicking on the title bar and now I have to go for the little arrow button. I initially thought moving the A/Z button was a mistake but it is more difficult to hit it by mistake in its new location.
I am not sure about the way the region names are displayed in PT8. I guess it is all part of the ‘smoother’ look but I find I am zooming in more just to read the region name as it is truncated so often. The fact that the default setting for the Edit window gri is on is a real pain for those of us for whom Grid is not part of our working day.
I would like to see a better set of appearance options than the existing contrast and saturation on the colour pallete so we can choose the shade of the background
Those are some of my thoughts, what do you think?