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iKlear

I used to use nanopure water ... roommate is a biology grad student and got a few gallons of this ultimate pure water :)

But recently, I got a gift card (which would have been better BEFORE i purchased a 17" MBP) ... so I bought the $30 iKlear kit. I will say, I was surprised at how well it worked. No streaks, but its important to follow the instructions and only do linear strokes. Circular cleaning doesn't work with iKlear :p
 
I tend to use a micro fibre cloth for my MacBook and my iPhone (and the iMac at work). Normally I just use some moist from my breath, but if I've gotten some more resilient smudges I break out the iClean.
 
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