If you read the Apple support forums you'll see this is a common problem for some Mac and PC users. It's not related to the computer OS, its a problem on the iPad.
Apple replaced my first one because of it, and my current one recently started having the same problem. Since I didn't have any data on mine that wasn't expendable i cleared all the data and added it back to iTunes. After wiping the iPad downloading more data (a movie and new photos) than it previously had, took less than 20 minutes. Prior to the wipe the "backing up" part of sync took over 3 hours to do 8 mbs of data.