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Totally depends on how much data you pile onto your drive. With all the **** I load and delete onto my drive I'd need to do it a bit more often. I'd say you'd notice when you need to do it.

Formatting and TRIM are not the same. You would not get the desired effect you're looking for simply by formatting the drive, save for possibly removing unwanted applications that were taking up CPU resources. The degradation of the SSD is not saved in anyway, however, by formatting the SSD. Infact, I believe it's the opposite.
 
I will say this about the 80GB drive in my MPB - it runs really cool - so much so that it seems to bring down overall heat in my laptop. My fan runs much less and at lower speeds than it used to.

That, and it's really fast.
 
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