Congrats on the nice article and the efforts you have put in it (you've got my 5). I have one comment on the model you have chosen - you assume that as far as the Tooltip is Alive, it is associated with a Win32 Handle (a simple property set like Active uses the SendMessage API). However, you may want to use it in certain cases (like Design-time) where Handle is not needed. Or you may want to instanciate it and display it later on. I think it is a good practise to create (and destroy) its Handle on demand (like System.Windows.Forms.Control does).