I've found that certain apps (Amazon MP3 and Stocks, for example) will occasionally be running in the background even when I've never once opened them. Why is this? This is not desirable - those CPU cycles are mine, not theirs!
Those apps come with the phone and can't be turned off or removed unless you root. Blame your carrier. There's really nothing you can do about it non-rooted. I feel your pain.
This goes with another post I made about a slightly different issue.
Background apps usually just respond to events. Events they care about, which is usually nothing for these sprint apps.
They take up RAM. HOWEVER unlike a desktop, when android wants ram it will remove anything in the "background" that it wants (older first) to free up space.\
The only exception to ram freeing up is when it sends notifications (a permanent icon in the notification bar... like a downloading icon from the market while the item is downloading).
So don't worry so much about it. These bloatware apps don't harm your android unless they do anything because batter is a big concern. Careful with facebook/twitter as they ping the service every few seconds, you can disable the "pinging" by just disabling the behavior, they won't do anything then. Even the messenger app might get removed from memory, when the system does a background synch it wakes up, loads, runs, and goes back to inactive.
The only thing I know of, like I point out, requires rooting the phone and voiding the warranty. Go to /etc/rcx.d and remove the associated file with the executable. (This, of course, assumes that the filesystem follows the same hierarchy as every other Linux distro I have run.)
Hope this helps!
Before rooting your phone, a not-so-easy operation, you should have a try to disable the auto launch when the phone restart.