If you going to use a App Killer, I strongly suggest Automatic Task Killer. Set the Task killer to kill the browser and Map, after a delay (1-5 minute).
The reason for this: Evo browser does not exist the page when you leave the browser, it just run your browser in the back ground. If the web page have things that automatically update every so often (ads, news feeds, etc) the browser will stay active in the back ground using up your battery for the CPU and 3G, and sometime even GPS. So I found that having ATK automatically kill your browser after you lock your screen is helpful.
I found the same to be true of Navigation also, if you forget to exist Navigation and left it running in your phone's back ground, it will kill your battery in no time.
So while I agree with most people that Froyo does a good job managing memory usage in general. There are legitimate reasons to use Automatic Task Killer in your Evo.