Fields pane item appearance
I love that display folders and hierarchies are now supported in BI Desktop. When you start building up a large number of tables, it quickly becomes difficult to distinguish which items are table names vs. fields in the columns. Also, the gray color of the display folders makes is slightly difficult to quickly identify the folders when you have a lot of things expanded.
The organization of the fields pane in Excel is a bit more clean... distinguishable display folder icon, clearly evident which lines are tables vs the attributes under them, display folders all get grouped together.
The fields pane in BI Desktop would be more user friendly if everything wasn't nearly the same shade of gray.
This has now improved with 2 different shades of grey, but still needs more contrast to make it easier to use. The visualizations pane is TERRIBLE! It's all the same colour so difficult to figure out what you are looking at.