Will still iTunes sync (but over wifi.) Gotta keep contacts and calendars updated. I make changes both on my phone and my iMac. Oh, and to pull photos/videos off the phone, too.
I'm pretty sure there is an option to only sync to iCloud over wi-fi so this should not effect your data usage.I prefer both, I might go to the Cloud, depends on Verizon honestly, I was grandfathered into unlimited but I hate that they throttle, we shall see.
Contact and Calendar can get sync wirelessly with MobileMe or the iCloud thats coming up.
I'm pretty sure there is an option to only sync to iCloud over wi-fi so this should not effect your data usage.