Have installed iTunes 10.5.1, as well as iOS 5.0.1, and the problem still persists. If there is nothing new to copy from iTunes to the iDevice, the sync goes quickly, with no 'Waiting' hangs. But if I put some new photos into iPhoto, which iTunes then needs to copy in the final step of the sync, then I get a very long 'Waiting for items to copy' before the photos are finally copied over.
It seems like the delay is down to the iDevice itself, because it's pretty consistently a 5-6 minute delay with the iPad 2 and an 11-12 minute delay with the iPhone 3GS, which roughly matches their difference in CPU speed.
I have no idea if the log entries in the Mac's syncservices.log file are significant, but I observed the following during a sync in which 23 new photos were (eventually) copied to the iDevices.
iPad 2 - 'Waiting for items to copy' took 6 minutes 7 seconds
15:12:53 - Step 7 of 7 - Waiting for items to copy
syncservices.log entries around that time:
2011-11-15 15:12:26:362|AppleMobileSync|2626|30ba30|Stats|Stats| com.apple.MobileSync.e6c48dabf4cba421b3dd1b24726688d0ae03d08b: fast sync com.apple.mail.Account
2011-11-15 15:14:26:473|SyncServer|2619|110ff0|Server|Info| Cancelling all sync plans.
2011-11-15 15:14:26:476|SyncServer|2619|110ff0|Server|Info| Goodnight, Gracie.
15:19:00 - Step 7 of 7 - Copying photo [1,2,3..] of 23
syncservices.log entries around that time:
2011-11-15 15:19:10:453|SyncServer|2638|110ff0|Logging|Info| Logging initialized, engine version 578.3 : log level 3
iPhone 3GS - 'Waiting for items to copy' took 11 minutes 18 seconds
15:27:13 - Step 7 of 7 - Waiting for items to copy
syncservices.log entries around that time:
2011-11-15 15:25:55:775|AppleMobileSync|2657|30ba30|Stats|Stats| com.apple.MobileSync.81ecb042684579c88e233990a46a496759dfbfdc: fast sync com.apple.mail.Account
2011-11-15 15:27:55:926|SyncServer|2651|110ff0|Server|Info| Cancelling all sync plans.
2011-11-15 15:27:55:929|SyncServer|2651|110ff0|Server|Info| Goodnight, Gracie.
15:38:31 - Step 7 of 7 - Copying photo [1,2,3..] of 23
syncservices.log entries around that time:
2011-11-15 15:38:41:676|SyncServer|2695|110ff0|Logging|Info| Logging initialized, engine version 578.3 : log level 3