Installed it on my 3GS... two days before my 5 arrived at my door.
Ever so slightly faster (on the 3GS), panorama photo is neat, maps are faster but need more info. The Do Not Disturb function is interesting, but as I'm already in the habit of putting my phone on vibrate and setting it face down on my night table before going to sleep, I find it not necessary for me.
On the 5, everything is blazing fast and smooth as one would expect. Unless you need the Google maps, do the upgrade.