It's been said - use 2. Crazy not to. Apart from the scrubbing which as oystein says will lose you at least 20% (often a lot more) if you only use one, you then also have a backup in case one goes down (or godforbid even goes under - stranger things have happened).
I voted though and will only say that had you asked me 12 months+ ago my vote would have ben completely different.
