The only forums I know of are:
– WPF Disciples; this is a great group because the um, disciples are experts but seems like 1/2 the posts are ‘inside’ comments between the um, disciples. By design, it is for mere mortals to observe only.
– WPF on Codeplex; useful but usually only by way of catching a new release of something. Discussion threads of interest are not easily located and it doesn’t seem as though response from knowledgeable responders comes often or timely.
– MSFT forums; noisy and confusing. More often than not an answer is repeated randomly and doesn’t address the question.
So I typically use SO as my first option to find an answer to a WPF type of issue. Where do you go online when you hit a WPF snag?
Just to be clear I mean by forums are places like SO where you can ask a question and get a response!
The forums on http://www.windowsclient.net is another good place where you can ask questions.
A great idea is to follow the WPF gurus/experts on twitter and then put your (short) questions across to them. Of course, there is no guarantee that they will answer, after all they lead busy lives too, but quite often they do.