Just going to put some helpful hints out there about this subject. The iPhone and iPod Touch are not really meant to be stand alone devices. They are meant to be paired with one single computer and synced at least once a week. The reason for syncing is to make a back up of the phone in case something happens to it. The iPhone and iPod Touch are great mobile devices and do anything you would probably need on the fly but still need a back up source.
When you sync the most important things you need to get is your contacts, calendar and pictures. Music,apps and movies can be replaced if truly need be but you can't go back in time and take that picture again. As you can see I'm focusing mainly on the iPhone users now so if you're an iPod Touch use just make sure you sync/back your phone up.
iPhone users need to understand something when you're on the iPhone or any smart phone for that matter...YOUR CONTACTS ARE NOT SAVED ON THE SIM CARD ANY MORE! You have to select somewhere to put the contacts. You can select outlook for PC, Address book for Mac and Gmail, Yahoo for both.
Please people sync your iPhone and iPod Touch. It will save you so many problems in the future.