private void Form1_Load(object sender, EventArgs e)
{
    _myData = new MyData();
    textBox1.DataBindings.Add("Text", _myData, "TheValue", false, DataSourceUpdateMode.OnPropertyChanged);
    textBox2.DataBindings.Add("Text", _myData, "TheValue", false, DataSourceUpdateMode.Never);
}

public class MyData : INotifyPropertyChanged
{
private string _theValue = string.Empty;

public string TheValue
    {
get { return _theValue; }
set
        {
if (string.IsNullOrEmpty(value) && value == _theValue)
return;

            _theValue = value;
            NotifyPropertyChanged(() => TheValue);
        }
    }

public event PropertyChangedEventHandler PropertyChanged;

public void NotifyPropertyChanged<T>(Expression<Func<T>> property)
    {
if (PropertyChanged == null)
return;

var memberExpression = property.Body as MemberExpression;
if (memberExpression == null)
return;

        PropertyChanged.Invoke(this, new PropertyChangedEventArgs(memberExpression.Member.Name));
    }
}