Steve,

Your comment about "when in doubt . . . " struck a nerve on me. I will agree with the "when in doubt, add the INT Identity colummn"; however, if you add a GUID as your identity column and make it a PK, then you have, essentially, made a random number your PK. Think that one through for a minute. A PK is, by default in the SQL Server world, a clustered index. Do you really want to use a random number to sort your table? Doesn't that sort of guarantee that the next entry that is made to the table is going to start causing fragmentation and/or resorting of the table?

IMHO, if you must use a GUID for your Identity column (and I will concede that there are times when that is the proper choice 😉 ) then you should make it a Unique Key/Index instead of a PK.