Now that I can watch all kinds of video and play all kinds of games on my phone, I realize that Flash on the phone drains the battery quicker, but not for the reasons you would expect. The reason was that I couldn't put it down. Having free access to all that stuff I was missing almost brought a tear to my eye. I spent more time using my phone than I ever had with my IPhone. My word of caution to people who are not able to try it first hand and have to listen to the media talk about it is that, when people say the battery drains faster, you really need to make sure that apples aren't being compared to oranges. Make sure that the reports are based on equivalent use of each device.
As I was playing around with it, I watched some videos on Adobe TV, played some of the games that were in the Adobe's Flash Showcase app and spend quite a while playing with it. Of course the battery went down slightly... very slightly. Nothing near the "OH MY GOD... I CAN HEAR THE BATTERY DRAINING BECAUSE IT IS DYING SO FAST" fud that is coming out of Apple. I was surprised at how little it actually affected the battery. Note that I was over WIFI, not 3G/4G so that probably would have an effect on battery life.
Overall I am very pleased with my EVO and Froyo so far. I will be posting about my experiences with it as I find new interesting things.
UPDATE: I said that Sprint "pushed" Froyo, but they actually didn't. They made it available for geeks like me to check for updates manually. If you can't wait, you can go into the Settings > System Updates > HTC Software Update menu.