It might be worth noting that the
Blues only go up to 750GB in storage space. Not exactly an optimal storage capacity if you're looking to minimise the number of drives used for storage. (Assuming you have that much to store, of course.)
The main advantage the Blue has over the Green (I just got lazy to type 'WD Caviar' after some time) is lower access latency; actual throughput varies quite a bit depending on lots of factors (disk model, number/density of platters, blahblah).
To illustrate, here's graphs showing the 1.5TB Green besting the 500GB Blue in read throughput.


They're only part of the story though. Of course, those graphs were intentionally picked for effect; for more details do your own googling or make a post in Technology.
[/geekdiarrhoea]