Martin,

Although I am a proponent of using surrogate keys there is one downside, that is the presense of a surrogate key often means that there is at least one other candidate key in the table design (that being the natural key). This requires that the Boyce-Codd Normal Form be applied making 3rd NF not quite good enough. Of course a surrogate key being always a single field obviates the need to apply 4th or 5th normal forms, which is why I suggest using surrogate kayes always. That along with E. F. Coods statement that, "Intelligent keys aren't".