The upgrade to iTunes 10.1 killed syncing my iPad. An 'Unknown error 0xE800000A' dialog was displayed. Searching Apple support, where the problem has occurred before without a fix beyond rebooting the device, and searching for the error on the web also didn't give a solution that worked.
Checking in the Console showed that iTunes couldn't write to a plist file in /var/db/lockdown; the file already existed and belonged to _usbmuxd. A quick Terminal session with:
cd /var/db/lockdown
sudo rm the file name
using the file name of the problem plist followed by a restart cured the problem.
[crarko adds: I haven't tested this one. I hadn't heard of this issue before but searching for it indicates it has affected a number of people, using any kind of iOS device.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20101112200134531