Hi Odi,
In my experience of system development for financial institutions, this is a much needed feature.
Master-Child relationships are all very well and nice for showing the abilities of a grid, but I have rarely come across a user that prefers this presentation over a grid that shows the master detail side by side in "traditional report" fashion. Of course, here I am talking about small numbers of columns in each master/child datasource.
I disagree that it is more simply more 'spreadsheet like', I find that users also prefer it for report presentation. However, I will agree that the best examples of such presentation are commonly spreadsheet pivot tables.
A certain "other" grid developer supports it, however they don't yet have WPF control's. With the strong support within WPF of accessing the FrameworkElementFactory VisualTree should it not be a relatively easy implementation? I am thinking of a property "MergeAdjacentRepeatedValues", that for each column or row that when set to true will merge these cells, and non-repeat the titles. Even if this could be implemented only when disabling editing and all grid interaction, such as grouping and column dragging etc it would be a big feature advantage you will have over your current WPF grid competitor.
