I would like to suggest the ability to turn on/off a plus/minus icon that can appear in the grid header in order to expand all or collapse all.  This is one of those things that is not very difficult for people to code on their own, but it seems like a basic feature of a grid that can have child detail data.  I'd rather be able to set a boolean property through code or in my theme .skin file for the grid, and have it turned on for me.  It should function no matter what the HierarchyLoadMode is set to, but when set to "Client", the expand/collapse should all happen on the client.  Thanks!

Additional improvements for the MultiColumn Headers can be considered if needed:
1. Support for Header context menu
2. Client-side show / hide operations with the columns