You get NULL!
Well you get NULL when you don't cast. Say for example you do the following:
But when you do the following:
I didn't think the casting would be necessary, since according to the manual: http://msdn.microsoft.com/en-us/library/aa226054(SQL.80).aspx the datatype 'uniqueidentifier' has implicit casts with multiple data-types. But I guess it's just one of those things...