It has more features on the iPad than it does on the iPhone and it's easier to edit things on the large screen. I have it on my phone, but I was using it on my brother's iPad last night and it's even more impressive on the iPad.
iOS 5.1 also brings back the "Enable 3G" setting that some people used to improve battery life (by disabling 3G). However, if you're using a 4S on AT&T, you don't get it back. You are stuck with your lightning-fast 4G.
<conspiracy theory>Apple sure is letting AT&T get their way a lot these days! What's next? AT&T logo engraved on the next iPhone? </conspiracy theory>