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The MBA 13" screen is higher resolution which means Xcode may be slightly better as more elements can fit on the screen, the MBP has a better processor (at this exact moment) but the MBA has an SSD. The difference is negligible, it all comes down to preference and requirements, i.e. need of a superdrive
 
With regard to superdrive....

Is it possible to share out the iMac's superdrive, and access via LAN/wi-fi, as needed? I know it would be slow, but for the odd occasion, doable?
 
Yup, it's called DVD sharing. If you go to the MBA's spec's page, they mention it.
Without a built-in optical drive, how do you install new applications? Simply use DVD or CD Sharing. This convenient feature of Mac OS X lets you wirelessly “borrow” the optical drive of a nearby Mac or PC. So you can install applications from a DVD or CD and have full access to an optical drive without having to carry one around.
specs_remote20101020.jpg
 
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