Disabling mobile sync backup
Is there any way to disable iTunes making MobileSync backups on synchronization? I recently synced my iPad with a "new" netbook, and it took forever to do it. Later on, I thought it was weird that there were a few gigabytes of free space missing on the hard drive, and then I found that c:\Users\USERNAME\AppData\Roaming\Apple Computer\MobileSync\Backup\ holds around 5 GB of data.
I would like to perform a backup manually, on my "main" computer only, and only use sync (calendar, contacts...) on others -- which would also save time and disk space. How can I do it?