Knut Urdalen has come back to PHP-GTK2 (since trying it back in the alpha stage) and decided to give it a shot by porting over an application and seeing how easy it was.
I wanted to see how easy I can take a simple GTK application written in another language and port it to PHP-GTK2. I ended up porting this Ruby/Gtk example written by Daniel Lichtenberger which have some logic, dialogs, events and some graphics.
His experience was a pleasant one, finding that most of the code came over easily, if not directly (well, with syntax chnages, of course). There were a few issues with pulling in the graphics, but over all, it went well. If you'd like to check out the source for the game, you can download it here and (with PHP-GTK2 installed) run it with a simple "php tictactoe.phpw" command.