There is hell lot to learn in WPF. You need to die and reborn as a GUI programmer.
But is it worth the effort. Why?, Here is my answer.
Since you are asking this question, I assume you are Microsoft technologies based programmer.
As the direction of MS is towards WPF for GUI development, I see no choice. Win Forms will last long for probably 2 years more. Since the cool look and feel of WPF make users to ask for more and more WPF applications than Win Forms. As you know for many users GUI is the S/W :)
Now if you are non MS based programmer, probably from Java, I say WPF has lot of similarities with Java Swing. But it is a very-very big super set of Swing.
To have Swing catchup with WPF might take at least 2/3 years and by that time WPF might be ruling the word and I don't expect Swing to be much easier than this, if not difficult.
As silverlight is kind of platform independent and as it's model is similar to WPF, I predict WPF is going to rule at least for next 6/7 years if not a decade.
I believe and hope MS would make things much more easier for the programmers so that learning curve would be shortened or delegated to GUI artiists (using expression blend).
Hope I answered your question.