My first job after college, we created a healthcare app first using Gtk+ (crazy) with some insane SQL bindings to embedded Firebird database (my youth)... Eventually, after chatting with my brother and some other folks at Mozilla I decided XULRunner was the way forward. So while on a trip to Spain for 4 days I rewrote almost the whole app converting piles of Gtk+ C++ code into JavaScript and wrapping up our Firebird calls into XPCOM interfaces.

My main take aways from that experience...

1. Gtk+ is not a great choice at least in 2004 for Windows... but hacking the windows event loop is kinda fun.

2. Embedding C++ into JavaScript was amazing then and still now one of the coolest things about Ruby,Python,JavaScript is being able to write bindings in C/C++ so much fun.

3. XUL was at least in 2005/6 just not as good at rendering as HTML... and it kind of makes sense everyone was hammering away at HTML by browsing the internet. So while XUL had some really great tools, not being HTML meant it just never had the same amount of attention... and as CSS got better the layout abilities of HTML / CSS quickly became #1...