Ribbon control is fantastic in my opinion :-)

Here

http://windowsclient.net/wpf/wpf35/wpf-35sp1-ribbon-walkthrough.aspx

and here

http://elegantcode.com/2009/04/07/the-free-office-wpf-ribbon/

you can find a valid tutorial in order to make a cool UI.

Using the skin you can make cool UI for any cool user

http://www.codeproject.com/KB/WPF/SkinningInWPF.aspx

While play with WPF in multi thread scenario the following exception may be appears "Cross thread operation not valid".

At this link you can find a good way to avoid the above exception:

http://www.shabdar.org/cross-thread-operation-not-valid.html

At the same link you can find a cute tips to avoid the exception using th delegate.

http://javaflowswithin.blogspot.com/2010/03/c-threadsafecontrol.html

Actually, from my point of view, this is the right and light framework to implement the MVVM pattern in the WPF applications.

The toolkit is here available:

http://www.galasoft.ch/mvvm/getstarted/

Nice article about the multithreading way in the WPF forms.

http://elegantcode.com/2009/07/03/wpf-multithreading-using-the-backgroundworker-and-reporting-the-progress-to-the-ui/

I've used this article as startup, in my opinion I've choice to subclass the bw object.