I develop a WPF4 application and in my app I need to let the user select a folder where the application will store something (files, generated reports etc.).
Add The Windows API Code Pack-Shell to your project
using Microsoft.WindowsAPICodePack.Dialogs;
...
var dialog = new CommonOpenFileDialog();
dialog.IsFolderPicker = true;
CommonFileDialogResult result = dialog.ShowDialog();