While testing a workflow in CRM 4.0 we encountered the following situation.
The workflow runs when a custom entity is assigned to a person.
In this workflow a wait condition waits until a particular task is completed (activitystatus is completed).
The workflow never stops waiting, even when the task is completed.
You can imagine this is really annoying, I did a support call at Microsoft and after checking some settings, they told us this was a known issue and the were working on the fix.
A few days later we got the fix (KB951919), it is not in the public list of all CRM 4.0 updates and hotfixes, but there is a fix if you need it, just contact MS.
My thoughts exactly