We just switched from Env3s to Droids in our house, and love them. We've got 3 Droid Erises (not available now through verizon, but able to put on the plan) and one Motorola Droid (which is the expensive one.)
To save your battery, download the Advanced Task Killer Free, and use it to close apps that are sucking up battery power. I don't use the google apps, so I make sure those are closed. Also, you can turn the screen brightness down quite a bit without any noticeable difference. Mine is set at about 10-15% now, with auto adjust turned off, and I can't tell it's any much different than when it was set at full brightness.
Another thing I can do on my Eris is to have a widget on the main page that lets me turn off the network connection when I'm not using it. If I want to check my e-mail, get on the web, or go to the app marketplace, I can turn it on with one touch of my finger. The regular Droid doesn't come with this widget since it's specific to the HTC Eris. Maybe there's something in the marketplace to do the same thing, but I don't know.
Other things I do to save battery:
Turn off wi-fi unless I'm going to be using it.
Turn off bluetooth completely since I don't use it at all.
The first four days I had this phone, I didn't like it as much because the battery didn't last a full work day, even though I wasn't really doing anything at all with the phone other than a few short phone calls. Now that I've made these switches, the battery is lasting me at least four days, with me shutting the phone off when I'm in bed. And that includes me spending time surfing the Internet, checking my e-mail, and playing games while riding in the car on a two hour round trip drive.