you generally shouldnt store any "information" in a primary key. primary
keys are by definition immutable so SA would likely trip up if you change
them.
I'm not advocating SA support for this, but immutability isn't strictly speaking a necessary property of PKs.
Josh Berkus on this and other PK urban legends:
http://blogs.ittoolbox.com/database/soup/archives/007365.asp
--
Jonathan Ellis
http://spyced.blogspot.com
