Android apps don't "terminate" after you exit them (like iOS does, for example), they pause. This makes re-entering the app later significantly faster. From Android 2.0 (Eclair) onwards Android has used memory very efficiently. Prior to Eclair, task killers were required, as apps would continually run and slow down the phone. Task killers are a throwback to that time several years ago. These days, when task killers are used, they kill ALL tasks which requires that all of the system tasks then have to reload into RAM and run, draining your battery unnecessarily. This also means that your weather widgets stop working, your live wallpaper stop and so on...
Here is some interesting information on the problems with task killers
Instead of using task killers, try using Watchdog. In the cases of having poorly coded apps on your phone which can cause problems, Watchdog can identify these problem apps so that you can then uninstall them. This is far more effective than the use of task killers. If you don't want to pay for apps, there is even a "lite" version. More info here-
Also it should be known that in the Android OS, empty RAM is wasted RAM. When Android needs RAM it kills the oldest cached apps that are not actually running, but are instead sitting idle (or paused) in the background. If you are constantly killing apps to free up RAM, what is the point of having 512Mb of RAM?
If Android tells you that it is low on space, that is referring to your storage space, which is NOT the same thing as RAM. This is when you would move apps to your SD card or uninstall them if you don't use them.
With regards to the bloatware that is on the stock T-mo ROM, the use of Titanium Backup allows a rooted user to not only back up their apps (this is quite useful when changing ROMs), it also allows a used to "freeze" apps such as the bloatware on the stock ROM (although this is only available on the paid version).
There is more information about this here
Hopefully this will help clear up a lot of the common misinformation that is prevalent in the Android community and always remember, Google is your friend!
Research every claim that people make so that you can make yourself as informed as possible. This is the only way to stop the misinformation.