>>PMFJI -- here are the main advantage and disadvantages. The disadvantages are GUIDs take up more space and are slightly slower to process, neither of which is a major issue IMO. The advantage is GUIDs are guaranteed to be globally unique (that's what the G stands for), which can be important if data is spread across servers.
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>I'd like to see some numbers here - e.g. the performance difference with numbers. I guess they are available on the net and probably even here in UT, but may be you or someone can provide a direct reference.

On numerous occasions I've been forced to work with guids simply because I was interfacing with a 3rd party app or tool that used guids for PKs. In that case, it was an FK in my table. Only a couple of times have I chosen a guid as a PK in my app though and then only because it was in the requirements. I reallly didn't notice any performance degredation but then it would probably show up as the # of records grew ( > 100,000 as an example).