I looked at it, but couldn't see any benefit over Flash. SWFs compile once so with Python this allows for good cross-platform development (as with pyGTK), and using TCP/IP connection between the two means that desktop apps I develop can be deployed on web easily. (Maybe pyGTK can run in a browser, but I haven't seen that). There is more that can be done in Flash than pyGTK, and dozens of extensions, and a quick and easy GUI for prototyping (I admit I use scripting rather than components in final versions, but for quick design mockups its great to drag a button to the stage). Flash has good documentation, and there are lots of resources to use.
As with most things, it depends what you need the GUI to do, but for a web-based GUI run on a server in an n-tier setup with Python, I find Flash swfs does everything I've ever needed to do. I once tried to build the same GUI in Python, but found lack of being able to simply do simple things like layers, swapping depths, and so forth to be a real problem - at least for what I needed to do.
Have you tried Flash? (drag and drop the components, add a couple of lines of code, and its working).