If you attended Microsoft's PDC 2008 or if you have watched any of the WPF sessions from PDC 2008 on Channel9 you've probably heard of the WPF Toolkit. Here is the description of the toolkit from the CodePlex project site:
The WPF Toolkit is a collection of WPF features and components that are being made available outside of the normal .NET Framework ship cycle. The WPF Toolkit not only allows users to get new functionality more quickly, but allows an efficient means for giving feedback to the product team. Many of the features will be released with full source code as well. Over time, some of these features may be moved into the .NET Framework, based on readiness and customer feedback.
What is interesting about this Toolkit is that it offers Microsoft an opportunity to make controls available to the WPF community without the need to wait for a full .NET framework release. This is a great idea. However, it has some pitfalls that developers need to be aware of before adopting the toolkit.
If you watched the keynotes, you may have heard Scott Guthrie talk about the WPF Toolkit. He mentioned that it was being "released" and that developer's could start using it right away. Also, the dev status of the current release of the toolkit is listed as "Stable". However, after doing some research and asking a few questions in the Discussions forum I have found out that the toolkit really isn't ready for prime-time and probably will not be receiving any updates until the .NET 4.0 framework is released.
This is problematic because Microsoft has basically been pitching this at PDC and on developer blogs as something that is ready to use. There is a memory leak that affects both the VisualStateManager and the DatePicker and the DataGrid has a whole host of known issues. Given the current state of the WPF Toolkit and the knowledge that there will most likely not be any updates to it prior to .NET 4.0 (which won't be available until late 2009!), it is hard to recommend using the WPF Toolkit in production code at this time. It's a shame because all of the features in the Toolkit are very desirable. I'm really at a loss trying to figure out why Microsoft seems to have pushed this toolkit out in this state knowing that it would not be updated.
Moral of the story: If you are planning on using the WPF Toolkit for production code, make sure you are aware of the risks you are incurring.
UPDATE: Here is a link to one discussion thread where it is made clear that there will most likely not be any updates to the WPF Toolkit prior to the .NET 4.0 framework release: http://www.codeplex.com/wpf/Thread/View.aspx?ThreadId=38679 (There are more posts that state similar things that can be found on the CodePlex site under "Discussions")
UPDATE: I just realized that I didn't link to the article that got me thinking about this in the first place. Karl Shifflett, one of the WPF Disciples, blogged about the memory leak in the DatePicker on his blog at: http://karlshifflett.wordpress.com/2008/12/16/wpf-toolkit-datepicker-memory-leak-problem/