Please provide a property that will allow a message to be displayed to users when RadGridView is empty. 
Some users perception is that the program is not working properly when there is no data in the grid view so displaying a user-friendly message can be a useful way of preventing inquires and complaints.

GridViewCell.Errors - System.Collections.IEnumerable Errors { set; get; }

Errors collection always returns a collection of strings.  When using .NET 4.5 and INotifyDataErrorInfo the errors can be any type. In our case we are using a custom ValidationResult object that has different severity levels.

Because GridViewCell.Errors always returns strings and not the original underlying ValidationResult object our DataTemplate for ValidationResult is not applied.

All DragVisualProviders for the RadListBox, as described in http://www.telerik.com/help/silverlight/radlistbox-features-dragdrop.html, show as a bare minimum a horizontal line that clearly shows where the drop within the list will occur.

Unfortunately the RadGridView does not even have that out of the box for its DragVisualProviders, so dragging elements within a RadGridView provides no indication at all to where the drop will happen! This seems like a very basic feature the RadGridView should have to support dragging/dropping within it (which also seems like a very common functionality).

You can not select different filtering options through keyboard navigation. The only possible way to select a filtering operator from the list with available filtering operators is to click on it.

Add an option to clear all filters at once to the column filters.

Application hangs on start up if GroupRenderMode is set to Nested, there is a column with Width Star and a group descriptor applied.

When a gridview is placed in TabControl, the following CodedUI tests will fail:

Test 1. Click on a column header to sort by that column.

Test 2. Click on a drop-down button to filter a column.

Test 3. Drag a column to group by it. 

The workaround could be using QueryableCollectionView instead. Still, it does not suggest the exact same functionality as ICollectionView.

When the ScrollMode is set to Deferred, then only the vertical ScrollBar shows a position indicator. The same is requested on horizontal scrolling.

The group panel item image of a column with custom header is blurred

this is not related only to grid-inside-grid scenario (HierarchyChildTemplate), but also for a flat (classic) grid control. If you have a GridView and any other control (ex TextBox), you will notice that if you move focus from GridViewCell to TextBox, both