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My iPad does it's backup extremely fast, faster than my iPhone4 amazingly enough. The only time it has ever taken a long time is when I resynced my whole music collection with the 128kbps setting checked.

32G wifi iPad, 3.2.1, 13" MacBook Pro to sync with. Just a regular sync takes not even 30 seconds unless it's updating a bunch of apps.
 
It takes good 6 hours for me and I suspect it has something to do with my hobby of constantly trying out apps and causing the contents change all the time... I rarely backup nowadays.
 
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