Intermittent Sync w/ihone 3GS

I am having a curious problem with my new iPhone. When hooked up to any USB port on my MacBook, it might sync/charge or it might not. I have used every port to chase this problem down. I have also switched cables. The only reliable way I have right now to charge the phone is the power adapter that came with the phone. I'm getting slightly perturbed because i am constantly updating my address book and I need to sync. Any help would be great.

Thanks,
Ron Scott