the new 2008 booksonline has a lot of stuff on MERGE and EXCEPT

http://technet.microsoft.com/en-us/library/bb510625.aspx

the neat thing is how it has clauses for WHEN MATCHED and NOT MATCHED:, when the merge finds a match, based on the criteria, you know you need to update, if no match was found it must be new

USE AdventureWorks;

GO

-- Create a temporary table variable to hold the output actions.

DECLARE @SummaryOfChanges TABLE(Change VARCHAR(20));

MERGE INTO Sales.SalesReason AS Target

USING (VALUES ('Recommendation','Other'), ('Review', 'Marketing'), ('Internet', 'Promotion'))

AS Source (NewName, NewReasonType)

ON Target.Name = Source.NewName

WHEN MATCHED THEN

UPDATE SET ReasonType = Source.NewReasonType

WHEN NOT MATCHED BY TARGET THEN

INSERT (Name, ReasonType) VALUES (NewName, NewReasonType)

OUTPUT $action INTO @SummaryOfChanges;

-- Query the results of the table variable.

SELECT Change, COUNT(*) AS CountPerChange

FROM @SummaryOfChanges

GROUP BY Change;