I was under the impression that you do not need to put in a GUID column, has that changed in 2008?. If you set-up Sql Server to replicate it will add the GUID column(s) it needs behind the scene and manage them. You do not need to plan for them nor program for them. You can use ints for your keys. The only issue you have with uniqueness is within your own keys if you allow external data stores to import records.