Jeroen and Chris,
'Tis most definately worth the effort. Actaully, there's very little effort involved.... if you know PHP relatively well, you're on your way. Much of the learning curve is actually working with the GTK methods themselves, not the PHP. Assuming that you've got some experience with GTK programming, the main thing to remember is that classes must be instantiated by reference
$new_window = &new GtkWindow();
for example and unlike C/C++, you don't specify the target widget in a method's argument list, rather the methods and called in PHP OOP style:
$new_window->set_title("This is a sample title");
gtk.php-coder.net is a great resource to start with. Some nice tutorials, some sample code, and links to a few off site apps. I've also got a sample app up on my site which you might find interesting, a relatively simple mp3 database app I wrote a few weeks ago as an experiment in the new bind. It provides insert, update, select, delete and search functionality on both mySQL and ODBC-compliant db's like MS Access, SyBase, IBM DB2, etc. The link is:
http://www.mithril.ca/code/php-gtk+/mp3_gtk.php
Hope this helps!!!
Cheers,
Geoff A. Virgo