You know.. this is troubling me too.. that is to say.. I know how you can check and close running apps.. and I love that you can run up to 6 apps at once.. that's great. But when you hit the HOME button, I assumed it closed the app. Shuts it down. I am wondering how do you switch between running apps.. is there some sort of indication on the app icont that it's running? As an Android developer (just starting out), I see there is ways to listen fo hooks that an app is "paused', etc.. so you can pause a game (er.. I as a developer can write code that when signaled, I pause the game, stop the music, etc). I know you can go into the settings and in the About Phone or something you can see running tasks, close them down, etc. You can get a free app to list tasks and kill them as well. I am just really curious how do I run 2 games, 3 apps, and a background task all at once?
It's a common misunderstanding about the 6 app thing. When you press and hold the home button, it shows you the last 6 apps you have run. This has NOTHING to do with what apps are currently running in memory. In fact, al lot more than 6 apps and services can be running in the background. It's just a quick way for you to see and restart a recently accessed app.
To truly see what is running in memory and kill the apps you can download an app from the Market such as TasKiller (free or paid) or Advanced Task Killer, etc. Those apps will show what is running and let you kill them. I use the free TasKiller and it even shows how much memory is freed up as you close apps. Remember that after you have killed all desired tasks, also kill TasKiller so it isn't using memory in background.
Android should also be able to kill things on its own as the memory is needed for other things, but it's not perfect.
There's also a new option to kill services within Adroid. From Home menu, press Menu button, choose Settings, Applications, Running Services, then you can press on services and stop them. Services are different from Apps so you will probably still want to use a program such as TasKiller. I put the TasKiller shortcut on my home screen so it is easy to access.