Thom just published a post about the removal of the Exchange workflow designer from the Exchange downloads.  And I just posted my comments about troubleshooting the workflow engine in Exchange.  :)

Here's the link to the Exchange API-spotting post about this:

http://blogs.msdn.com/exchangedev/archive/2007/05/15/microsoft-office-workflow-designer-for-exchange-is-no-longer-available.aspx

I have to say that I saw this coming with the release of Exchange Server 2007 and the lack of workflow libraries.  Really though, I think in the long run for developers of workflow enabled applications it's a great thing. The new strategic direction is a more direct and much more robust solution that what we can offer with just the Exchange workflow designer.

Here's the reasoning behind this:

"There are several reasons why moving away from Exchange Workflow and the Workflow Designer for Exchange, and moving to WF is the right thing:

- WF is Microsoft’s strategic direction for workflow applications.

- WF leverages current technology and a better programming model.

- WF can be used in managed code (ExWFD and CDOWF cannot).

- WF will also be used in other Microsoft applications.

- ExWFD and CDOWF are not compatible with Microsoft Exchange Server 2007."

So as it's noted in Thom's post, if you are planning to develop any new workflow projects, you should really start investigating the new Workflow Foundation that's now available.  He's also gone ahead and added a bunch of links and resources to get you started in that direction.