How can I use HTML + Javascript to build a python GUI?
If you are thinking about real desktop applications that are multi-threaded and/or use multiple system component - forget about JavaScript. That requires a very good SDK (like PyQt4), and not a basic wrapper like Appcelerator Titanium. Note that developing such applications takes a lot of time.
Second option is to drop the desktop binding and make a web application with an advanced frontend UI made with one of JavaScript frameworks & friends (Ember, Angular... up to things like dhtmlx and alike widgets). Those can't use system components (like access some hardware), but they can provide nice services.
I have been experimenting with Appcelerator Titanum yesterday and I think it's cool when it comes to Javascript.  
Python features on Appcelerator Titanum are so limited (can't use some modules for example).  
My question is How can I use html & javascript as a GUI tool for a real python application ? 
I am running windows 7 and i was thinking of using webkit for that purpose but couldn't know how to work with it in python.  
I am planning to make a standalone executable using py2exe as I don't know if the users always have python and the appropriate modules installed.