Try it in PrepareViewStyleInfo. This worked for me.
private void Form1_Load(object sender, System.EventArgs e)
{
this.gridControl1[1,1].Text = "SomeText in Cell 1,1";
this.gridControl1[2,1].Text = "SomeText in Cell 2,1";
this.gridControl1[1,2].Text = "SomeText in Cell 1,2";
this.gridControl1[2,2].Text = "SomeText in Cell 2,2";
this.gridControl1.PrepareViewStyleInfo += new GridPrepareViewStyleInfoEventHandler(gridControl1_PrepareViewStyleInfo);
}
private void gridControl1_PrepareViewStyleInfo(object sender, GridPrepareViewStyleInfoEventArgs e)
{
if(e.ColIndex > 0 && e.RowIndex > 0)
{
e.Style.CellTipText = e.Style.Text;
}
}