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Those who've JB'd their phones and run SBSettings can tell you that shutting down apps from the multitasking bar absolutely DOES free memory, because we have an easily accessible tool that tells us how much is in use vs. available at any point. Close the multitasked apps and watch your available memory climb. Obviously, doing things like shutting down unneeded Safari windows reclaims even more.

I've not experienced the freeze described, but I'm also still on 4.0. Personally, I routinely shut apps down as much for convenience in accessing those I'm actively multitasking with as for reclaiming memory.
 
I've had it happen a few times on my iPhone 4. But it only freezes for about 15-20 seconds.

My 3G did it half the time I used the fast app switcher.
 
Mine always used to freeze right after closing the messages app when closing a lot of apps at once. It may be the same for you. Keep an eye out on which app you close last before it freezes.

After I jailbroke my phone, I don't seem to have the problem anymore.
 
Mine always used to freeze right after closing the messages app when closing a lot of apps at once. It may be the same for you. Keep an eye out on which app you close last before it freezes.

After I jailbroke my phone, I don't seem to have the problem anymore.


THAT'S IT!! MESSAGES APP IS THE PROBLEM, it's the same for me!
 
Messaging isn't it...

I've had the same problem for weeks, Verizon iPhone 4 on 4.2.6
It's definitely not messaging. I've had most of the freezing happen after closing Nightstand so I thought it was that but after playing around with opening and closing multiple apps it seems random. I've had it freeze on just about everything at this point (I always keep phone and messaging open, and usually Facebook too)
 
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