Sprint may have oversold the practicality of 4G at this point. Time will tell.
I don't know about that. 4G is great when you want to use it as a hotspot for laptop(s). You'll likely be able to charge phone while using hotspot.
But in-phone, the only benefit I'm seeing is high quality video and video chat - neither of which I use often. I do notice a significant bump downloading apps from the market but it's not like 3G is unbearable. More 4G specific apps will come now that the capability is there. WiFi hotspot is where 4G is very useful for me in the meantime.
Edit: Forget that the best indirect benefit of 4G is simultaneous voice/data thanks to separate radios.
For me, the real benefit to 4G, eventually, will be simultaneous voice and data. But that's only a real benefit if you can leave 4G on. Tethering is something I do rarely, but checking something online while on a call could be handy.
4G will use more power consumption than WIFI. however most of the apps in your phone are configured to execute tasks only when a WIFI connection is enable. As a result, you might see an increase of battery drain when your phone is in WIFI.