** This issue is addressed in ArcGIS 9.0 Service Pack 2 (SP2) **
If a model contains MakeTableViews, it can be run once to obtain the correct output. Running it a second time results in the output's fields becomming mix-matched between the processes.
When building a model, and then specifying a field name for a parameter; for example, CalculateField, Statistics, and so forth, the model can be run. Subsequent runs do not work because the validated list of fields is incorrect, making it difficult to use that model.