Comment 2 for bug 242288

So :)

The long and the short of this is that overlaying something on top of the widget isn't going to work. Unless my understanding of Gtk is completely wrong, it would always be racing with the terminal widget itself to redraw.

However, after using OS X's terminal.app I realised that they put the size in the titlebar all the time, so I decided to do the same.
As a result, revision 721 in trunk introduces this feature. If you have the titlebars enabled, you will always see the size of that terminal!