How do you manage your multi-tasked apps in 4.0+?

Obviously, Apples version of multi-tasking puts every app you open in the multitask bar.

Does leaving them in there make a performance difference? I'm guessing 99% of them are in a suspended state, so does the phone know the difference?

Do you bring up the bar and close them after using them? Do you close them a few times a day? Do you only clear them once a day? Never?