The grips on the scrollbar's thumb is blurred on 120dpi as well as some of the borders.

As it turns out, we hit a WPF specific problem with 120 DPI. The issue is similar to the following:
http://connect.microsoft.com/VisualStudio/feedback/details/798513/wpf-dpi-rendering-issues-with-two-borders
For the time being this issue is not addressed and most probably would not be fixed.