If you are using the persistence service in Windows Workflow Foundation (WF) you may experience failures in the Delay activity to fire it's completed event. This can be worked around in WF but not in SharePoint workflows. We now have KB932816 article describing the problem and how to obtain a fix from Microsoft.
This fix applies to workflow in Windows Workflow Foundation and also in Windows SharePoint Services 3.0 and in Microsoft Office SharePoint Server 2007.
Here is the original post. Paul is a GREAT resource for WF. Thanks Paul!