It seems that most authorities agree that dark or otherwise prominent gridlines in plots are "chartjunk" by any reasonable definition and distract the viewer from the message in the main body of the chart. So I won't bother to give references on that point.
Equally, we can all agree that there will be times that pale gridlines to create a reference for viewers will be necessary. Tufte argued the need for(and used) gridlines occasionally, as pointed out for example in this article. And I agree with the Hadley Wickham's approach in ggplot2 to make such gridlines white on a pale grey background, when you need to use them.
What I am uncertain about however is whether such gridlines and grey background should be the default, as they are in ggplot2. For example, there seems to be no reason for the grey background other than to case the white gridlines into relief - which further begs the question of whether either is needed. I have recently started using ggplot2 for most of my graphics needs and think it is awesome, but it has challenged my "no box, no background, no gridlines" approach to graphics that I used before. I used to think that gridelines=OFF should be my default unless there is a particular reason for adding them in - basically the approach recommended in this article, for example.
Of course, it is straightforward to define a theme in ggplot2 to avoid the gridlines and background shading (and in fact we have done this at my work), but ggplot2's approach is so awesome and generally its default aesthetic choices are good that I wonder if I am missing something.
So - I would be grateful for any references on this point. I am sure it has been well thought through (for example by Hadley Wickham in setting the ggplot2 defaults) and I am very open to being pointed in the right direction. The best I've been able to find is a couple of links on the ggplot2 google group but the most helpful looking reference by Cleveland isn't available at the link given.