I realize it is a small thing, but the error message for a duplicated key value that was recently updated to include the key value implies that it is a single culprit. This was fixed based on https://connect.microsoft.com/SQLServer/feedback/details/470542/duplicate-key-values as far as I can tell. It is a great change with just a minor confusng bit.
So if I have a UNIQUE constraint on the following table on the otherColumn
INSERT INTO test.testErrorMessage (testErrorMessageId,otherColumn)
You get the following:
Msg 2601, Level 14, State 1, Line 1
Cannot insert duplicate key row in object 'test.testErrorMessage' with unique index 'UXtestErrorMessage'. The duplicate key value is (Third).
But there was two duplicated key value. This could get frustrating to a novice user. This could be fixed since it is not production yet, but it would be stuck in eternity otherwise