I have sent my Caviar Black 500gb for warranty last month, and i just got information that WD is sending me WD7500AALX which is Caviar Blue, with much shorter warranty to 31.05.2013.
Hi yes it is do not take a blue drive as a replacment for a black one. The blue drive has 8 meg cache 5400 rpm the black has 16 meg cache 7200 rpm that is the laptop 2.5 version. The desktop drives your black has the same cache and rpm as the blue they offered you so would be about the same speed but still the black drives are supposed to be made better.