So it seems that when you run an app and hit the Home button to leave the app, it continues to run in the background.
And you have to remember to bring up the Multitasking window pane at the bottom to really quit it so that it does not eat up CPU and data/Wifi, etc in the background.
Is there not a better way to really QUIT the app while you're in it so you dont have to constantly (and remember) to bring up the window pane to manually close all your apps?
I have to "lol" at the guy from "tech support". As a software developer I have a lot of experience with these people and how much they think that they know.
To the original question; I assume you are on iOS5; the recently used apps bar does just contain a list of recently used applications on the device, and there is no real way to see (without using another app) which is using resources on the device.
I believe you can notice some sluggish behaviour when you have lots of apps there because when you press the home button, an app will reside in memory still. Eventually, you might open up an app that needs 100MB memory and, instead of that memory being free, the device has to first free up some memory starting with the oldest app that is on the recently used list that's still in memory that isn't active.
This process doesn't remove those apps from the list. So a slight sluggish behaviour can be the device freeing up some RAM for your app to run.
When you do press the home button on an app, unless the developer has used the appropriate API, the maximum time an app can stay active for is 4 seconds, after that time it is suspended in memory. Some apps that use the API necessary like Skype can maintain the use of certain device functions like audio or data.
There is no native way to see which are active and which are suspended unless you know the app. There are very few that do remain active.
I find the quickest way to "close" the apps en masse to free up memory manually and make sure nothing is running (except native apps like mail and iPod and SMS) I find is, instead of closing the left most app, then waiting for all the apps to shuffle along, you can close them from right to left quicker. You can also close 2 at once if you build up the skill.
You could restart the device, this keeps the apps in recently used; but they all enter the stopped state, so no memory usage.
I'm surprised though you have noticed the time the device spends recovering memory because it's usually very quick unless you are opening a big app.
I hope this helps. If it doesn't I hope you have your answers.
But never belies that apps on the recently used bar are killing your battery or anything like that unless it's Skype and you've only just closed it.