We also have another grid (the Microsoft one) and in that one for resizing a vertical line is drawn to indicate the size of your column. Only when you release the mouse is the column actually resized. I think this is better for the performance of the grid. In the attachment you can see what I mean.

ADD. RadGridView - add support for self-reference hierarchy for child levels as well

Make possible users easily to change the behavior of replacing the null value with empty string.

Workaround: 
DataTable table = new DataTable("table");
table.Columns.Add("ID", typeof(int));
DataColumn col = table.Columns.Add("Name", typeof(string));
col.AllowDBNull = false;
col.DefaultValue = string.Empty;
table.ColumnChanging += new DataColumnChangeEventHandler(table_ColumnChanging);
this.radGridView1.DataSource = table;

private void table_ColumnChanging(object sender, DataColumnChangeEventArgs e)
{
    if (!e.Column.AllowDBNull && (e.ProposedValue == DBNull.Value || e.ProposedValue == null) && e.Column.DataType == typeof(string))
    {
        e.ProposedValue = string.Empty;
    }
}

Consider the iTunes Artist mode grid
http://www.telerik.com/forums/itunes-like-grid

Allow setting the CurrentColumn/CurrentCell in the RowValidaging event

IMPROVE. RadGridView - In hierarchy the excel-like filtering on child levels to show values only from the rows of the expanded row instead of all rows of the template.

Depending on when the ViewDefinition is applied RadGridView throws an exception or not

Improve the user experience by adding marker which shows the position where the group element will be added.

Currently it is not possible to hide the horizontal scrollbar of child views in RadGridView and to use a single root level scrollbar.

The total summary rows have the same number of indent columns as the group summary rows and it makes them harder to distinguish.

Currently when using RadGridView in AutoSizeRows mode, only the cells that are visible determine the row height.

Currently it is possible to localize only menu names that appear in expression editor list, not in the expression itself.

The user should be able to select just part of the text in read-only grid using mouse.

Row reorder feature not work in unbound mode RadGridView with self-reference hierarchy

When the RadGridView is bind to a data source, which contains a flagged enum, an instance of GridViewComboBoxColumn should be added and its editor should be checked drop down list.

Currently the mixed hierarchy mode does not work for child templates

IMPROVE. Extend the functionality of formatting the group text when grouping by more than one column is performed on the same group level

When you are using drop down list in RadGridView in suggest-append mode, you should be allowed to add non-existing item to the data source.

To reproduce: 
1. Run the attached sample project.
2. Move the form to the right bottom of the screen.
3. Hover a cell to show the tool tip. It will start blinking. Please refer to the attached gif file.

Workaround: use screen tips: http://docs.telerik.com/devtools/winforms/telerik-presentation-framework/tooltips-and-screentips/screen-tips

To reproduce: 
1. Add a RadGridView with a GridViewCheckBoxColumn and enable the paging functionality for it.
2. Toggle the header checkbox on the first page. Only the rows from the page are toggled.

Workaround: you can subscribe to the HeaderCellToggleStateChanged event and toggle all rows:

 private void radGridView1_MouseUp(object sender, MouseEventArgs e)
 {
     if (this.radGridView1.Tag+""=="toggle")
     {
         this.radGridView1.Tag = null;
         this.radGridView1.HeaderCellToggleStateChanged -= radGridView1_HeaderCellToggleStateChanged;
     }
 }

 private void radGridView1_MouseDown(object sender, MouseEventArgs e)
 {
     RadCheckBoxElement element = this.radGridView1.ElementTree.GetElementAtPoint(e.Location) as RadCheckBoxElement;
     if (element != null && element.Parent is GridCheckBoxHeaderCellElement)
     {
         this.radGridView1.Tag = "toggle";
         this.radGridView1.HeaderCellToggleStateChanged += radGridView1_HeaderCellToggleStateChanged;
     }
 }

 private void radGridView1_HeaderCellToggleStateChanged(object sender, GridViewHeaderCellEventArgs e)
 { 
     this.radGridView1.BeginUpdate();
     foreach (GridViewRowInfo row in this.radGridView1.Rows)
     {
         row.Cells["Discontinued"].Value = e.State;
     }
     this.radGridView1.EndUpdate(); 
 }