I've noticed that there are some differences between several controls regarding watermark styling and left padding. It becomes quite visible if you put them next to each other. The left column only contains watermarkcontent and the right one contains text. I'm using the Windows7Theme but it looks the same in several other themes aswell.
<StackPanel Orientation="Horizontal"> <StackPanel Width="200" HorizontalAlignment="Left"> <telerik:RadWatermarkTextBox Margin="3" WatermarkContent="RadWatermarkTextBox"/> <telerik:RadAutoCompleteBox Margin="3" WatermarkContent="RadAutoCompleteBox"/> <telerik:RadMaskedTextInput HorizontalAlignment="Stretch" Margin="3" EmptyContent="RadMaskedTextInput" TextMode="PlainText"/> <telerik:RadComboBox IsEditable="True" Margin="3" EmptyText="RadComboBox"/> </StackPanel> <StackPanel Width="200" HorizontalAlignment="Left"> <telerik:RadWatermarkTextBox Margin="3" Text="RadWatermarkTextBox"/> <telerik:RadAutoCompleteBox Margin="3" SearchText="RadAutoCompleteBox"/> <telerik:RadMaskedTextInput HorizontalAlignment="Stretch" Margin="3" Value="RadMaskedTextInput" TextMode="PlainText"/> <telerik:RadComboBox IsEditable="True" Margin="3" Text="RadComboBox"/> </StackPanel></StackPanel>