Subclassing "Not inteded for subclassing"

[Simen Haugen]

I see dwt also have the "Not intended for subclassing", but the classes 
are not marked final.
It shouldn't be any problems subclassing as long as you're careful, right?

Right now I want to subclass Text and automatically add a dynamic 
tooltip. The same type of text box should be used many places in my 
application. I know I can just bind each time, but is it really 
dangerous to do this kind of subclassing to save typing?

Or is there a easier way to solve these kind of things?