I had the same problem, reordering controls in a Grid based layout is a real pain.
So I've wrote a custom panel that does "form layout" (groups of two columns, all labels same size, all control same size,everything aligned, etc.), it's on my blog at: http://www.nbdtech.com/Blog/archive/2010/07/27/easy-form-layout-in-wpf-part-1-ndash-introducing-formpanel.aspx