Im currently running an early release of Froyo (CM6 Cyanogen) on my EVO and it will be almost as if you have a new phone. Im sure there will be slight variations in everything that is included from Moto and Verizon compared to what Cyanogen includes, but here are just a few things.
1. JIT really will make it fly. Speed and zippiness of scrolling and opening apps and browsing is just insane. Lag just doesn't exist on any level.
2. There are so many automatic options now. Saving apps to SD is an automatic function and you can set it to automatically do it, or you can control it to move only specific apps. You can also move apps from internal to SD really easy.
3. In the market when you have app updates, you can update them all at the same time with the push of one button.
4. The stock browser is totally different, im still trying to figure out how to do things, but its faster and definately has more options. Inculded with flash 10.1 is just incredible.
There are other things im not including because im not sure if its just a cyanogen thing, or froyo thing so I don't wanna speak to whether Moto/Verizon is including those options or not. But you will love it, thats all i can say.
My benchmarks in my sig are listed just to show what kind of jump in performance im seeing just on a pre release ROM. An official release is probably only gonna make them increase more.