<p>I'm <em>considering</em> migrating my c# application from using custom GDI+ drawn controls to a WPF application with custom controls etc. I would like to know what's involved and what to expect.</p>

<p>Are there any resources people can recommend that might help? Or indeed any personal experiences that might be beneficial?</p>

This is actually a project i am working on at the moment although I have been lucky enough to be able to start again. If you can do this I would strongly recommend it, obviously keeping the core functionality of the old system/controls but start afresh. It is always nice to start from a base and to know where things went wrong/right previously.
Personally i have found the
msdn website
extremely useful, if not stackoverflow is a very good place for knowledge. I would be happy to give pointers if you need any.
Also if you ever have any questions about databinding this is the place to go:
bea costa
she has covered most stuff there.
On an extra note we have experienced a huge improvement in performance with using wpf over GDI.