I had made some questions regarding php-gtk(there are only 4 php-gtk tagged questions and 3 are mine) and I end up answering myself because no one answer them.
I know is a strange language selection but I was attracted to it because it runs on several OS's and the fact that I can reuse some of my code (also the apps end up looking good and I can make little installers in NSIS that just rocks).
Is there a better alternative, that is free(as freedom) and can run on several platforms?
Does it have to be GPL, or are other open source solutions acceptable? Python has much more mature GTK integration and it's open source but not GPL. You can bundle python scripts into an executable with a runtime. You can generate these executables for many platforms including Windows.
Both Python and Ruby can work with the GTK libraries. These may be better chocies of languages for you (you'll certainly get more folk here answering your questions :)
See http://stackoverflow.com/questions/115501/is-ruby-any-good-for-gui-development and http://stackoverflow.com/questions/115495/is-python-any-good-for-gui-development for links for Ruby and Python respectively.
To answer the first part of your question. Yes - I use php-gtk. This could be the start of a beautiful friendship.