The battery is what it is. If you use it a lot, even with tweaks, you're not going to make it a full day with one charge. I have chargers everywhere -- at work, at home, and in my car. So I plug whenever I can. If I know I will have an extended time away from a charger, I carry a spare battery with me and it works out great for me, but YMMV. Because I'm recharging all the time, I hardly need the spare during the day. But once I get home, I'm on the Evo constantly, and the spare battery allows me to power through non-stop. Having a spare battery and charger means you never have to take a break to charge the phone. You can get a battery and charger combo for under $12 shipped from eBay. Note that the Touch Pro 2 and the Hero and the Evo all use the same exact battery when you're shopping around.
As for lag -- define "lag". I think that for some people, the screen transitions when you swipe to the next or pinch and zoom look a bit choppy next an iPhone or even a Hero. It doesn't bother me at all, but it's really important to other people. But the lag you get on Galaxy phones when you go back to the home screen is non-existent in the Evo -- it's a very, very snappy phone, and the capacitance buttons respond quickly, and they never go to sleep on you.
Evo has froyo, so you can watch Flash videos in the browser. One little talked about froyo feature is the ability to set an independent password protected lock screen. So I can set the password protection to go on after 30 minutes of non-use, which means I can lock the screen and unlock it inside of a 30 minute window without having enter my PIN each time. I was reluctant to use a PIN lock code because of the hassle of re-entering the PIN code each time. But I use the PIN code now since it only activates after long periods of inactivity.
Oh, and no GPS issues to speak of on the Evo.