We are all insane. I'm not really sure if we program because we are insane, or if we are insane because we program. The scary part is how people think programming is so modern and advanced an industry while programmers gets more and more frustrated due to the un-developed processes and tools used. Just think about what "Assembly line" means in IT compared to other industries, and you start to realize we have a problem.
My advise is as follows:
1) Simple GUI, need a result fast, short term project or willing to reprogram the GUI later: WinForm
2) Simple GUI, want to learn and willing to spend the time it takes: WPF with current tools
3) Anything else: Wait for better WPF tools, anything else is a waste of time.
I am currently fighting though 2), and it is a hell. Should probably have gone for 3).
Forget about graphics libraries etc:
1) You would be programming for the past, not the future. As we can never keep up with what we would like to do, we have to aim ahead. When we finally get something done, we normally find we are already behind anyway.
2) They separate graphics from controls. That can't be done if you want a decent object model of your GUI.