You have started what is known as "yet another task killer discussion". If you use the search engine, you can find several spirited threads.
Bottom line: uninstall that crap. Don't worry about tasks that are sitting idly in memory. Don't worry about stock apps running at startup. If an app you download is taking up too many resources just uninstall it. When done with Navigation, choose exit from the menu. When done with maps, return to the home screen to stop GPS.
Here's some more stuff I just happen to have in my "clipboard":
1) DON'T listen to the guy at VZ and your cousin about how you need to kill tasks
2) DON'T use the stock email client. Use the Gmail app, K9, or touchdown
3) Download other browsers, like Dolphin HD and xscope, and set user agent to Desktop/Computer
4) Watch out for the GPS icon in the notification bar at the top. It really uses battery power. When you are done with Navigation, choose Exit from the menu. When done with maps, press your phone's Home button to tell it to stop using GPS
5) When installing apps, watch what privileges you are granting! Why is your wallpaper asking to access your contacts? Also watch for stuff that runs on startup, including widgets, which can take a toll on battery charge.
6) Try to find your answer using a search engine
