I'd like to see something in this that allows for parallel workflow so the same object is allowed to be in more than one place at a time, in more than one state. I'd also like to see a graphviz or dia interface to this so the workflow is nicely visualized.
I regularly use the first concept when implementing workflow-using applications, the second is a nice thing I've liked from Lotus Workflow. See a screenshot at Here is a screenshot of something that was created in a Visio-like editor.
Otherwise, nice job. How tied is this to SPOPS or can the persistence layer be swapped for other things? How about sub-processes? Once you have multiple workflow processes running they may need to interact. For example - employee changes process may require a network access request which would have its own workflow which may drive other processes, etc.