On the iPhone there isn't a whole lot of obvious difference - the only big thing is you can now assign individual tones to text messages from particular contacts. Airprint is very useful but the default config is rubbish - it'll only print to certain HP wireless equipped printers. I got a little tool called
printopia which adds all my Mac's printer to the airprint available printers list. It does work pretty well, in fact.
The big change is on the iPad, which has now 'caught up' with the iPhone. All the cool stuff like multitasking, app groups etc that iPhone users (well, newish iPhone users) have been taking for granted, we finally got.
Jon