Well, I have been suffering for a long time from this issue. Every time I want to syn my iTouch wiht my mac, it takes ages. After googling a bit for a solution, it is straightforward:
1. - Quit iTunes.
2. - Open Terminal.app
3. - Copy and paste this in, then hit return:
defaults write com.apple.iTunes AutomaticDeviceBackupsDisabled -bool true
4. - Copy and paste this in, then hit return:
defaults write com.apple.iTunes DeviceBackupsDisabled -bool false
5. - Open iTunes
6. - Plug in your iPhone (2.0 or 3G) and sync.
