I've used Backgrounder lots when I've run my iPhone jailbroken (and still do on the iPad) – but it doesn't help at all on a stock iPhone of course.

What you've said on RAM and battery makes sense to me. Wouldn't it be lovely if Apple would document this somewhere? Maybe they have and I just don't know where to look I guess.

As for choosing which apps are allowed to multitask, this can be controlled with the latest version of Backgrounder (for jailbroken phones, of course). Backgrounder let's you choose, on a per-app basis, whether an app should be allowed to background, and whether it should do so using Backgrounder's method or the built-in iOS4 method.

Since it says that the least recently used app is deleted when memory is low, that means that the app must be held in RAM. RAM needs power in order to keep its current state, otherwise we would never have to boot up our computers. That said, there is SOME battery drain in multitasking, although the exact amount is likely small.

Regardless, I too would like to be able to choose what is "backgrounded." I was in Vegas this weekend and didn't have an iPhone charger. While killing everything except the phone via SBSettings was helpful, I felt like I had to go into the dock and quite all of the backgrounded apps, because when the iPhone battery is as bad as it is, every bit of juice helps.

Also, why can't I use YouTube "backgrounded?" I often use it to access music that I can't find elsewhere and it should be able to function like the iPod or Pandora.

I believe they do. I've looked at SBSettings on my 3GS on iOS 4 and can clearly see 14 apps being held in memory at one time (leaving me with about 40 MB out of the 130 or so initially available). I very, very rarely experience any slowdowns, though.

I'm aware of how you can manually close an app via the multitasking bar and in fact posted an article about it yesterday. I have not seen any place yet where it is clearly stated whether or not suspended apps utilize any memory or battery resources though. If you have, please share a link.

Yup, I'm aware of how the system is setup to shutdown apps completely when required. This is part of why I'm left with the question about what sort of resources are being used by 'paused' apps.

I like using Twitter and Facebook (from time to time), albeit, I don't think I want them running all the time. I like my battery for texting, and browsing forumslogs, etc, etc 🙂

"Suspending" an app — which is really just saving the state for fast switching back to it — does not use up any battery life, as far as I know. If an app uses one of the seven services that are available in the background, then it probably does use battery life. For example, pandora. I assume, however, that Pandora in the background uses the same battery life that the iPod running in the background would have used previously.

Also, you can disable background processing for apps on a one-off basis. You tap and hold on an icon the switcher tray, and then you can hit the minus sign to shut it down. The only time I have done this so far is with GPS apps. If you launch TomTom and then quit back to the home screen, I believe it continues to work in the background so that it can provide directions. As far as I can tell, the only way to shut it down is to tap the minus sign next to its icon in the switcher tray.