// A custom formatter object.
public class BaseFormatter : IFormatProvider, ICustomFormatter {
    // The GetFormat method of the IFormatProvider interface.
    // This must return an object that provides formatting services for the specified type.
    public object GetFormat(Type format) {
        if (format == typeof (ICustomFormatter)) return this;
        else return null;
    }
    // The Format method of the ICustomFormatter interface.
    // This must format the specified value according to the specified format settings.
    public string Format (string format, object arg, IFormatProvider provider) {
        if (format == null) {
            if (arg is IFormattable)
                return ((IFormattable)arg).ToString(format, provider);
            else
                return arg.ToString(); 
        }
        if (format == "B")
            return Convert.ToString(Convert.ToInt32(arg), 2);
        else
            return arg.ToString();
    }
}

// ...
// Assign the custom formatter to the editor.
spinEdit1.Properties.DisplayFormat.FormatType = FormatType.Custom;
spinEdit1.Properties.DisplayFormat.FormatString = "B";
spinEdit1.Properties.DisplayFormat.Format = new BaseFormatter();
spinEdit1.Properties.IsFloatValue = false;
spinEdit1.EditValue = 10;

' A custom formatter object.
Public Class BaseFormatter : Implements IFormatProvider, ICustomFormatter
    ' The GetFormat method of the IFormatProvider interface.
    ' This must return an object that provides formatting services for the specified type.
    Public Function GetFormat(ByVal format As Type) As Object _
    Implements IFormatProvider.GetFormat
        If format.ToString() = GetType(ICustomFormatter).ToString() Then
            GetFormat = Me
        Else
            GetFormat = Nothing
        End If
    End Function

    ' The Format method of the ICustomFormatter interface.
    ' This must format the specified value according to the specified format settings.
    Public Function Format(ByVal formatString As String, ByVal arg As Object, _
    ByVal provider As IFormatProvider) As String Implements ICustomFormatter.Format
        If (formatString = Nothing) Then
            If TypeOf arg Is IFormattable Then
                Format = CType(arg, IFormattable).ToString(formatString, provider)
            Else
                Format = arg.ToString()
            End If
            Exit Function
        End If
        If (formatString = "B") Then
            Format = Convert.ToString(Convert.ToInt32(arg), 2)
        Else
            Format = arg.ToString()
        End If
    End Function
End Class

' ...
' Assign the custom formatter to the editor.
SpinEdit1.Properties.DisplayFormat.FormatType = FormatType.Custom
SpinEdit1.Properties.DisplayFormat.FormatString = "B"
SpinEdit1.Properties.DisplayFormat.Format = New BaseFormatter()
SpinEdit1.Properties.IsFloatValue = False
SpinEdit1.EditValue = 10