In iOS, you'll receive SMS-style notifications when a VIP e-mails you, and those VIP designations will sync up over iCloud to your Mac and other iOS devices. You'll always be able to tell which contacts are VIPs by the star next to their name. Also, you'll now be able to add photos and videos to messages in iOS much more easily, which I consider a godsend. The fact that there isn't an attachment button in the compose e-mail window already is mind-boggling.
There are a ton of new features in iOS 6; be sure to check 'em out over here!