Make internal use of BindingGroup in DataGrid optional
Validation is already complex in WPF and the obligatory use of BindingGroup in DataGrid makes validation inconsistent if not buggy. See the numerous complaints on "datagrid validation" on Microsoft Connect. BindingGroup is an unfortunate UI-centric transaction mechanism. AFAIK SL can do even do without it.
I'd rather have a transaction mechanism based on a temporary, custom build clone object like in dialog windows. Contrary to the BindingGroup this would work neatly with a 'fully interactive' viewmodel and MVVM.