Just tried Tango on my Evo with my friend who has an Epic and IMO it's so much better than Fring.
* It looks similar to iPhone's FaceTime, which I like, because the video of the other party is in full screen and the video of yourself is a little thumbnail in the bottom corner of the screen.
* You can also swap between the front facing camera and the rear camera by tapping the "camera swap" icon at the top of the screen.
* Video and audio quality is much clearer and smoother than Fring (though I wish the audio could be a little bit louder)
It's still a little buggy, but that's expected because it's still in its early stages of development. There has been a few times the video of the other party froze (but I was still able to hear them) and as others mentioned, it's currently a battery drainer.
A few things I hope they'll implement soon:
* landscape mode support (so I can make use of the Evo's kickstand

)
* ability to turn on the LED Flash when using rear camera
* ability to video call Skype users