Honestly? Not a thing! Even though the Kies software is rubbish and it took me ages to get syncing with Outlook sorted out, I am absolutely in *love* with this phone. Most fun I've had in years! I've fiddled with everything to the n'th degree, making it just exactly how I want it. I love the screen - the extra size is great for those of us with eyesight that's ...*cough*... getting on in years. I love the speed. I - most of all - love the freedom. Can't see me ever going back to Apple.
I'd say, if you just want to pick it up and use it, maybe downloading a few apps... Well, the Samsung is just better hardware and every app I wanted I found (or found functionally the same thing). I have a friend like that, not in the least techie, and she loves hers.
If you're at all of the geek persuasion, you're going to be in Nerd Heaven.
A fiddler and poker's paradise.