The iPhone Camera Roll can cause increased backup and restore times in iTunes if not properly managed. It's easy to mismanage the Camera Roll if you--like me--use it store media for showing later to friends or family. Apple did not intend the Roll to be used this way, however, and recommends that users use the Photo app, instead, for storing media you plan on showing off later.
Per this support document, whenever you sync or perform a restore in iTunes, the app creates a backup of the contents of your iPhone. The more pictures, screen snapshots, or video you have stored on the Camera Roll, the longer a backup or restore takes.
The solution to the problem is easy: Make sure that you regularly import the contents of your Camera Roll, delete that content, then sync the content that you must have in your pocket back to the iPhone using iTunes. I had nearly 200 media files in my iPhone 3GS Camera Roll and deleted all of these after syncing and importing using iPhoto on my Mac. I used iTunes to restore content that I needed into the Photo app and I saw an immediate decrease in the time it took my iPhone to back up. Apple provides detailed information on performing these tasks in their support document for Mac OS X, Windows XP, and Windows Vista.
This simple housecleaning effort will reduce the number of media files in your Camera Roll and significantly improve backup and restore times in iTunes. It certainly did for me and it is possible that properly managing your Camera Roll would resolve the issue I wrote about previously where users were plagued by missing photos on their iPhones.
It remains to be seen whether iTunes 9, annouced today, will help resolve this problem in a more elegant manner. Stay tuned.