One is that any design model has its limitations (even a spiral one). To make the assumption that a single model covers all design situations is what has led to harsh criticism of model-based approaches in general (for ISD models see a summary of this debate in Gordon and Zemke’s (2000) The Attack on ISD and Zemke and Rossett’s (2002) A Hard Look at ISD.

Different situations require different approaches to the design process. If you are in company with great creative freedom, then a completely open spiral approach might be appropriate. But, in a highly regulated environment, a more stepwise approach might be more appropriate. This does not mean that iterative activity is not occurring in both situations only that the type of guidance needed is different.

Another issue with models is how we view the purpose of the model itself. Is it supposed to be a step-by-step instruction guide for the designer? Is it intended to educate or communicate to managers, end users? Is it supposed to provide general guidelines on an approach? Or is it intended to assist project managers accurately determine resource needs? Is the model used to accurately describe how design occurs or prescribe real activities?

As a designer, I want to know the following about any process model (cf. Reigeluth, 1999 on instructional design theory).
1. What are the implicit values the model builder holds?
2. In what context is the model most appropriate?
3. How to particular methods vary based on specific situations in which the model is implemented?

Of course, answering these questions requires a degree of formative research and this is not usually done on a formal level for many models.

My second comment is on the learning process (which Kathy extends from her design model). Learning is an extremely complex phenomenon that people have been trying to understand for years. Analogous to the issues with design models, learning is facilitated (i.e. instruction) in different ways for different people. Complicating the matter even further, learning occurs for the same person in different ways at different times. This means that what is motivating for someone (or for different people) at one point might actually be annoying or hinder learning at another. I have seen folks from an HCI background (my doctoral minor) make this same mistake. The techniques for assessing a quality UI are not the same as the assessing whether learning or better performance is achieved after an instructional event. We want instruction to be engaging but, even if it is not, it does not mean that no learning occurs.

Again, interesting posts and I look forward to reading more from this blog.

References

Carroll, J. M. (1992). Minimalist documentation. In H. D. Stolovitch & E. J. Keeps (Eds.), Hanbook of Human Performance Technology (pp. 331-351). San Fransisco, CA: Jossey-Bass.

Gordon, J., & Zemke, R. (2000, April 2000). The Attack on ISD. Training, 42-53.

Reigeluth, C. M. (1999). What is instructional design theory and how is it changing? In C. M. Reigeluth (Ed.), Instructional-design theories and models volume II: A new paradigm of instructional theory.Mahwah, NJ: Lawrence Erlbaum Associates.

Zemke, R., & Rossett, A. (2002). A hard look at ISD. Training, 26-34.